net: use DEBUG_NET_WARN_ON_ONCE() in __release_sock()

Check against skb dst in socket backlog has never triggered
in past years.

Keep the check omly for CONFIG_DEBUG_NET=y builds.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NJakub Kicinski <kuba@kernel.org>

net/core/sock.c

@@ -2844,7 +2844,7 @@ void __release_sock(struct sock *sk)
 		do {
 			next = skb->next;
 			prefetch(next);
-			WARN_ON_ONCE(skb_dst_is_noref(skb));
+			DEBUG_NET_WARN_ON_ONCE(skb_dst_is_noref(skb));
 			skb_mark_not_on_list(skb);
 			sk_backlog_rcv(sk, skb);