net: Add skb_queue_walk_from() and skb_queue_walk_from_safe().

These will be used by TCP write queue handling and elsewhere.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d2f1778..a19ea43 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1571,6 +1571,15 @@
 		     skb != (struct sk_buff *)(queue);				\
 		     skb = tmp, tmp = skb->next)
 
+#define skb_queue_walk_from(queue, skb)						\
+		for (; prefetch(skb->next), (skb != (struct sk_buff *)(queue));	\
+		     skb = skb->next)
+
+#define skb_queue_walk_from_safe(queue, skb, tmp)				\
+		for (tmp = skb->next;						\
+		     skb != (struct sk_buff *)(queue);				\
+		     skb = tmp, tmp = skb->next)
+
 #define skb_queue_reverse_walk(queue, skb) \
 		for (skb = (queue)->prev;					\
 		     prefetch(skb->prev), (skb != (struct sk_buff *)(queue));	\