netpoll: zap_completion_queue: adjust skb->users counter

zap_completion_queue() retrieves skbs from completion_queue where they have
zero skb->users counter.  Before dev_kfree_skb_any() it should be non-zero
yet, so it's increased now.
Reported-and-tested-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJarek Poplawski <jarkao2@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/netpoll.c

@@ -215,10 +215,12 @@ static void zap_completion_queue(void)
 		while (clist != NULL) {
 			struct sk_buff *skb = clist;
 			clist = clist->next;
-			if (skb->destructor)
+			if (skb->destructor) {
+				atomic_inc(&skb->users);
 				dev_kfree_skb_any(skb); /* put this one back */
-			else
+			} else {
 				__kfree_skb(skb);
+			}
 		}
 	}