Support Virtua Racing in NetPlay

[michael-myers]

Tested using two macOS 12.1 systems running RetroArch 1.9.14 and Genesis Plus GX v1.7.4 33aef5e, and the same rom file of Virtua Racing (USA region edition). Of about a hundred or two hundred other titles I tested in Netplay, this is one of only two to have an Netplay problem (the other one being Super Skidmarks, but its problem is probably a separate and unrelated issue).

It's not a surprise to me that Virtua Racing might present special challenges, due to its on-cart Sega Virtua Processor (SVP). But, Genesis Plus GX core emulates the single player experience just fine, including save state and load state functions. It seems like it's only NetPlay that has a problem.

What happens is that the guest connects to the host, and after a couple of seconds, only sees a black screen. So after about the first title card (text on screen) it goes black. There are no pop-up overlay messages indicating any kind of error.

Is there maybe additional RAM state related to the SVP that needs to be incorporated into NetPlay state syncing?