net: add common accessor for setting dropcount on packets

As part of an effort to move skb->dropcount to skb->cb[], use
a common function in order to set dropcount in struct sk_buff.

Signed-off-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/sock.c b/net/core/sock.c
index 93c8b20..9c74fc8 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -466,7 +466,7 @@
 	skb_dst_force(skb);
 
 	spin_lock_irqsave(&list->lock, flags);
-	skb->dropcount = atomic_read(&sk->sk_drops);
+	sock_skb_set_dropcount(sk, skb);
 	__skb_queue_tail(list, skb);
 	spin_unlock_irqrestore(&list->lock, flags);