[SK_BUFF]: Introduce skb_network_header()

For the places where we need a pointer to the network header, it is still legal
to touch skb->nh.raw directly if just adding to, subtracting from or setting it
to another layer header.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/xfrm6_mode_beet.c b/net/ipv6/xfrm6_mode_beet.c
index c015bfd..247e2d5 100644
--- a/net/ipv6/xfrm6_mode_beet.c
+++ b/net/ipv6/xfrm6_mode_beet.c
@@ -67,7 +67,7 @@
 		goto out;
 
 	skb_push(skb, size);
-	memmove(skb->data, skb->nh.raw, size);
+	memmove(skb->data, skb_network_header(skb), size);
 	skb_reset_network_header(skb);
 
 	old_mac = skb_mac_header(skb);