SV_SpawnServer: Register netgame-advertised servers with the MS

This is done in a different location in the previous entry in the series, but the author of this commit couldn't find it.
Since we're using the 2.2 codebase, it's been put where they have it instead.

src/d_clisrv.c

@@ -4226,6 +4226,11 @@ boolean SV_SpawnServer(void)
 				I_NetOpenSocket();
 			}
 
+			if (cv_advertise.value)
+			{
+				RegisterServer();
+			}
+
 			ourIP = 0;
 			STUN_bind(GotOurIP);
 		}