net: Add skb_unclone() helper function.

This function will be used in next GRE_GSO patch. This patch does
not change any functionality.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Eric Dumazet <edumazet@google.com>
diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
index 0c3fadd..7ed78c9 100644
--- a/net/sched/act_pedit.c
+++ b/net/sched/act_pedit.c
@@ -131,8 +131,7 @@
 	int i, munged = 0;
 	unsigned int off;
 
-	if (skb_cloned(skb) &&
-	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		return p->tcf_action;
 
 	off = skb_network_offset(skb);