These diagnostics are supposed to guide the user to problem resolution.
They're displayed if no packet is received from the server within one
second of connecting.
No message if we don't have STUN servers.
"Trying to determine UDP connectivity..." if no answer has been received
from the STUN server yet and it hasn't timed out yet.
"UDP seems to be filtered." if the STUN request has timed out.
"UDP and TCP IP addresses seem to be different. Try disabling VPN,
proxy or network accelerators." if the STUN request has returned an IP
address different from the one obtained via HTTP from info2.ddnet.tw.
"No answer from server yet." otherwise, if the STUN request has returned
no interesting data, indicating that it's likely the game server's
fault.
