Discontinue dependency on remote socket address

[m-ronnblom]

pafd depends on the XCM socket's remote address being available.

The address is used for observability purposes, and to decide how to do map connection to a user (e.g., for access control purposes).

The remote address is not available on XCM v1.9.0, in case the UX transport is being used, and the peer does not enable the SO_PASSCRED socket option. This socket option is always enabled by libxcm, but other XCM-compatible peers may not.

For access control purposes, the "xcm.transport" attribute should be used.