Fix motd being broken for admins

It turns out the game was sending the full size of the motd buffer (254) rather than just the size of the string made, therefore sending a load of garbage and making the game apparently execute unknown or illegal net commands

src/d_netcmd.c

@@ -2965,7 +2965,7 @@ static void Command_MotD_f(void)
 		}
 
 	if ((netgame || multiplayer) && client)
-		SendNetXCmd(XD_SETMOTD, mymotd, sizeof(motd));
+		SendNetXCmd(XD_SETMOTD, mymotd, i); // send the actual size of the motd string, not the full buffer's size
 	else
 	{
 		strcpy(motd, mymotd);