af_unix: Set drop reason in unix_sock_destructor().

unix_sock_destructor() is called as sk->sk_destruct() just before
the socket is actually freed.

Let's use SKB_DROP_REASON_SOCKET_CLOSE for skb_queue_purge().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250116053441.5758-4-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/unix/af_unix.c

@@ -640,7 +640,7 @@ static void unix_sock_destructor(struct sock *sk)
 {
 	struct unix_sock *u = unix_sk(sk);
 
-	skb_queue_purge(&sk->sk_receive_queue);
+	skb_queue_purge_reason(&sk->sk_receive_queue, SKB_DROP_REASON_SOCKET_CLOSE);
 
 	DEBUG_NET_WARN_ON_ONCE(refcount_read(&sk->sk_wmem_alloc));
 	DEBUG_NET_WARN_ON_ONCE(!sk_unhashed(sk));