UDP fixes
Created by: trond
Fixed a couple of issues with PacketPeerUDP:
- recvfrom was getting wrong buffer sizes causing disconnects.
- recvfrom could get wrong buffer sizes due to signed<->unsigned conversion.
- disconnects were caused by WSAECONNRESET-error, which normally should be ignored (the udp chat example is difficult to try on Windows due to this). I did not do anything in the posix implementation with this, as I'm not sure if it's an issue there - not able to test right now.