stop checking disconnected _lastSock

[JAndrassy]

WiFiServer was checking _lastSock forever. It slowed down the sketch.
This PR sets _lastSock to NO_SOCKET_AVAIL if firmware reports the 'sock' as disconnected.

EDIT: In a sketch with other TCP connections (client connections, other server) the 'sock' stored in _lastSock maybe reused and then without this fix, the server would return some unrelated client connection. It still can happen if the 'sock' is reused before this fix detects that it was disconnected

[github-actions]

Memory usage change @ 62cff51

Board	flash	%	RAM for global variables	%
arduino:mbed_nano:nanorp2040connect	🔺 0 - +8	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:megaavr:uno2018:mode=on	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrvidor4000	🔺 0 - +8	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrwifi1010	🔺 0 - +8	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:nano_33_iot	🔺 0 - +8	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/AP_SimpleWebServer flash	%	examples/AP_SimpleWebServer RAM for global variables	%	examples/ConnectNoEncryption flash	%	examples/ConnectNoEncryption RAM for global variables	%	examples/ConnectWithWEP flash	%	examples/ConnectWithWEP RAM for global variables	%	examples/ConnectWithWPA flash	%	examples/ConnectWithWPA RAM for global variables	%	examples/ConnectWithWPA2Enterprise flash	%	examples/ConnectWithWPA2Enterprise RAM for global variables	%	examples/ScanNetworks flash	%	examples/ScanNetworks RAM for global variables	%	examples/ScanNetworksAdvanced flash	%	examples/ScanNetworksAdvanced RAM for global variables	%	examples/SimpleWebServerWiFi flash	%	examples/SimpleWebServerWiFi RAM for global variables	%	examples/Tools/CheckFirmwareVersion flash	%	examples/Tools/CheckFirmwareVersion RAM for global variables	%	examples/Tools/FirmwareUpdater flash	%	examples/Tools/FirmwareUpdater RAM for global variables	%	examples/Tools/SerialNINAPassthrough flash	%	examples/Tools/SerialNINAPassthrough RAM for global variables	%	examples/WiFiChatServer flash	%	examples/WiFiChatServer RAM for global variables	%	examples/WiFiPing flash	%	examples/WiFiPing RAM for global variables	%	examples/WiFiSSLClient flash	%	examples/WiFiSSLClient RAM for global variables	%	examples/WiFiStorage flash	%	examples/WiFiStorage RAM for global variables	%	examples/WiFiUdpNtpClient flash	%	examples/WiFiUdpNtpClient RAM for global variables	%	examples/WiFiUdpSendReceiveString flash	%	examples/WiFiUdpSendReceiveString RAM for global variables	%	examples/WiFiWebClient flash	%	examples/WiFiWebClient RAM for global variables	%	examples/WiFiWebClientRepeating flash	%	examples/WiFiWebClientRepeating RAM for global variables	%	examples/WiFiWebServer flash	%	examples/WiFiWebServer RAM for global variables	%
arduino:mbed_nano:nanorp2040connect	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0
arduino:megaavr:uno2018:mode=on	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:samd:mkrvidor4000	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0
arduino:samd:mkrwifi1010	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0
arduino:samd:nano_33_iot	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	8	0.0	0	0.0

Click for full report CSV

Board,examples/AP_SimpleWebServer<br>flash,%,examples/AP_SimpleWebServer<br>RAM for global variables,%,examples/ConnectNoEncryption<br>flash,%,examples/ConnectNoEncryption<br>RAM for global variables,%,examples/ConnectWithWEP<br>flash,%,examples/ConnectWithWEP<br>RAM for global variables,%,examples/ConnectWithWPA<br>flash,%,examples/ConnectWithWPA<br>RAM for global variables,%,examples/ConnectWithWPA2Enterprise<br>flash,%,examples/ConnectWithWPA2Enterprise<br>RAM for global variables,%,examples/ScanNetworks<br>flash,%,examples/ScanNetworks<br>RAM for global variables,%,examples/ScanNetworksAdvanced<br>flash,%,examples/ScanNetworksAdvanced<br>RAM for global variables,%,examples/SimpleWebServerWiFi<br>flash,%,examples/SimpleWebServerWiFi<br>RAM for global variables,%,examples/Tools/CheckFirmwareVersion<br>flash,%,examples/Tools/CheckFirmwareVersion<br>RAM for global variables,%,examples/Tools/FirmwareUpdater<br>flash,%,examples/Tools/FirmwareUpdater<br>RAM for global variables,%,examples/Tools/SerialNINAPassthrough<br>flash,%,examples/Tools/SerialNINAPassthrough<br>RAM for global variables,%,examples/WiFiChatServer<br>flash,%,examples/WiFiChatServer<br>RAM for global variables,%,examples/WiFiPing<br>flash,%,examples/WiFiPing<br>RAM for global variables,%,examples/WiFiSSLClient<br>flash,%,examples/WiFiSSLClient<br>RAM for global variables,%,examples/WiFiStorage<br>flash,%,examples/WiFiStorage<br>RAM for global variables,%,examples/WiFiUdpNtpClient<br>flash,%,examples/WiFiUdpNtpClient<br>RAM for global variables,%,examples/WiFiUdpSendReceiveString<br>flash,%,examples/WiFiUdpSendReceiveString<br>RAM for global variables,%,examples/WiFiWebClient<br>flash,%,examples/WiFiWebClient<br>RAM for global variables,%,examples/WiFiWebClientRepeating<br>flash,%,examples/WiFiWebClientRepeating<br>RAM for global variables,%,examples/WiFiWebServer<br>flash,%,examples/WiFiWebServer<br>RAM for global variables,%
arduino:mbed_nano:nanorp2040connect,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0
arduino:megaavr:uno2018:mode=on,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:samd:mkrvidor4000,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0
arduino:samd:mkrwifi1010,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0
arduino:samd:nano_33_iot,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,8,0.0,0,0.0

[LisaRowell]

This is tangentially related to issue #176 and if that were fixed, aka the whole _lastsock mechanism removed, I believe this would be fixed as well.