net: use helpers to change sk_ack_backlog

Writers are holding a lock, but many readers do not.

Following patch will add appropriate barriers in
sk_acceptq_removed() and sk_acceptq_added().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ax25/ax25_in.c b/net/ax25/ax25_in.c
index dcdbaee..cd6afe8 100644
--- a/net/ax25/ax25_in.c
+++ b/net/ax25/ax25_in.c
@@ -356,7 +356,7 @@ static int ax25_rcv(struct sk_buff *skb, struct net_device *dev,
 
 		make->sk_state = TCP_ESTABLISHED;
 
-		sk->sk_ack_backlog++;
+		sk_acceptq_added(sk);
 		bh_unlock_sock(sk);
 	} else {
 		if (!mine)