amt: fix memory leak for advertisement message

When a gateway receives an advertisement message, it extracts relay
information and then it should be freed.
But the advertisement handler doesn't free it.
So, memory leak would 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

@@ -2698,9 +2698,8 @@ static int amt_rcv(struct sock *sk, struct sk_buff *skb)
 				err = true;
 				goto drop;
 			}
-			if (amt_advertisement_handler(amt, skb))
-				amt->dev->stats.rx_dropped++;
-			goto out;
+			err = amt_advertisement_handler(amt, skb);
+			break;
 		case AMT_MSG_MULTICAST_DATA:
 			if (iph->saddr != amt->remote_ip) {
 				netdev_dbg(amt->dev, "Invalid Relay IP\n");