Fix buffer overflow when setting a NETVAR string CVar

There was a possible buffer overflow if you tried setting a console var
that had the CV_NETVAR and that was of the string type.
The overflow would happen if you were trying to set the console variable
while in a multiplayer / netgame state.

This commit just increases the size of buf to account for everything
that needs to be written to it.

src/command.c

@@ -1992,7 +1992,7 @@ static void CV_SetCVar(consvar_t *var, const char *value, boolean stealth)
 	if (var->flags & CV_NETVAR)
 	{
 		// send the value of the variable
-		UINT8 buf[128];
+		UINT8 buf[512];
 		UINT8 *p = buf;
 
 		// Loading from a config in a netgame? Set revert value.