skb: Add skb_head_is_locked helper function

This patch adds support for a skb_head_is_locked helper function.  It is
meant to be used any time we are considering transferring the head from
skb->head to a paged frag.  If the head is locked it means we cannot remove
the head from the skb so it must be copied or we must take the skb as a
whole.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index e1f8bba..c199aa4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1699,7 +1699,6 @@
 			      struct splice_pipe_desc *spd, struct sock *sk)
 {
 	int seg;
-	bool head_is_locked = !skb->head_frag || skb_cloned(skb);
 
 	/* map the linear part :
 	 * If skb->head_frag is set, this 'linear' part is backed by a
@@ -1710,7 +1709,7 @@
 			     (unsigned long) skb->data & (PAGE_SIZE - 1),
 			     skb_headlen(skb),
 			     offset, len, skb, spd,
-			     head_is_locked,
+			     skb_head_is_locked(skb),
 			     sk, pipe))
 		return true;