net: Add skb_queue_is_last().

Several bits of code want to know "is this the last SKB in
a queue", and all of them implement this by hand.

Provide an common interface to make this check.

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

include/linux/skbuff.h

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4a144e8..3a5838d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -473,6 +473,19 @@
 }
 
 /**
+ *	skb_queue_is_last - check if skb is the last entry in the queue
+ *	@list: queue head
+ *	@skb: buffer
+ *
+ *	Returns true if @skb is the last buffer on the list.
+ */
+static inline bool skb_queue_is_last(const struct sk_buff_head *list,
+				     const struct sk_buff *skb)
+{
+	return (skb->next == (struct sk_buff *) list);
+}
+
+/**
  *	skb_get - reference buffer
  *	@skb: buffer to reference
  *