[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/ipv4/xfrm4_mode_transport.c b/net/ipv4/xfrm4_mode_transport.c
index a820dde..b198087 100644
--- a/net/ipv4/xfrm4_mode_transport.c
+++ b/net/ipv4/xfrm4_mode_transport.c
@@ -34,7 +34,7 @@
 
 	skb_push(skb, x->props.header_len);
 	skb_reset_network_header(skb);
-	memmove(skb->nh.raw, iph, ihl);
+	memmove(skb_network_header(skb), iph, ihl);
 	return 0;
 }
 
@@ -51,7 +51,7 @@
 	int ihl = skb->data - skb->h.raw;
 
 	if (skb->h.raw != skb->nh.raw) {
-		memmove(skb->h.raw, skb->nh.raw, ihl);
+		memmove(skb->h.raw, skb_network_header(skb), ihl);
 		skb->nh.raw = skb->h.raw;
 	}
 	skb->nh.iph->tot_len = htons(skb->len + ihl);