amt: fix possible memory leak in amt_rcv()

If an amt receives packets and it finds socket.
If it can't find a socket, it should free a received skb.
But it doesn't.
So, a memory leak would possibly occur.

Fixes: cbc21dc1 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/amt.c

@@ -2679,7 +2679,7 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 	amt = rcu_dereference_sk_user_data(sk);
 	if (!amt) {
 		err = true;
-		goto out;
+		goto drop;
 	}
 
 	skb->dev = amt->dev;