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/ipv6/ah6.c b/net/ipv6/ah6.c
index 3842331..bb02e17 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -521,8 +521,7 @@
 
 	/* We are going to _remove_ AH header to keep sockets happy,
 	 * so... Later this can change. */
-	if (skb_cloned(skb) &&
-	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		goto out;
 
 	skb->ip_summed = CHECKSUM_NONE;
diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index c674f15..b89a8c3 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -368,7 +368,7 @@
 	}
 
 	/* Head of list must not be cloned. */
-	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) {
+	if (skb_unclone(head, GFP_ATOMIC)) {
 		pr_debug("skb is cloned but can't expand head");
 		goto out_oom;
 	}
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index bab2c27..e354743 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -404,7 +404,7 @@
 		goto out_oversize;
 
 	/* Head of list must not be cloned. */
-	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(head, GFP_ATOMIC))
 		goto out_oom;
 
 	/* If the first fragment is fragmented itself, we split
diff --git a/net/ipv6/xfrm6_mode_tunnel.c b/net/ipv6/xfrm6_mode_tunnel.c
index 9f2095b..93c41a8 100644
--- a/net/ipv6/xfrm6_mode_tunnel.c
+++ b/net/ipv6/xfrm6_mode_tunnel.c
@@ -69,8 +69,7 @@
 	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 		goto out;
 
-	if (skb_cloned(skb) &&
-	    (err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
+	if (err = skb_unclone(skb, GFP_ATOMIC))
 		goto out;
 
 	if (x->props.flags & XFRM_STATE_DECAP_DSCP)