[NET]: Transform skb_queue_len() binary tests into skb_queue_empty()

This is part of the grand scheme to eliminate the qlen
member of skb_queue_head, and subsequently remove the
'list' member of sk_buff.

Most users of skb_queue_len() want to know if the queue is
empty or not, and that's trivially done with skb_queue_empty()
which doesn't use the skb_queue_head->qlen member and instead
uses the queue list emptyness as the test.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/llc/llc_c_ev.c

@@ -84,7 +84,7 @@ static u16 llc_util_nr_inside_tx_window(struct sock *sk, u8 nr)
 	if (llc->dev->flags & IFF_LOOPBACK)
 		goto out;
 	rc = 1;
-	if (!skb_queue_len(&llc->pdu_unack_q))
+	if (skb_queue_empty(&llc->pdu_unack_q))
 		goto out;
 	skb = skb_peek(&llc->pdu_unack_q);
 	pdu = llc_pdu_sn_hdr(skb);