wireguard: receive: remove dead code from default packet type case

The situation in which we wind up hitting the default case here
indicates a major bug in earlier parsing code. It is not a usual thing
that should ever happen, which means a "friendly" message for it doesn't
make sense. Rather, replace this with a WARN_ON, just like we do earlier
in the file for a similar situation, so that somebody sends us a bug
report and we can fix it.

Reported-by: Fabian Freyer <[e-mail]>
Signed-off-by: Jason A. Donenfeld <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/wireguard/receive.c

···
 		wg_packet_consume_data(wg, skb);
 		break;
 	default:
-		net_dbg_skb_ratelimited("%s: Invalid packet from %pISpfsc\n",
-					wg->dev->name, skb);
+		WARN(1, "Non-exhaustive parsing of packet header lead to unknown packet type!\n");
 		goto err;
 	}
 	return;