[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/decnet/dn_route.c b/net/decnet/dn_route.c
index 34079b7..32a7db3 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -386,7 +386,7 @@
 	__le16 tmp;
 
 	/* Add back headers */
-	skb_push(skb, skb->data - skb->nh.raw);
+	skb_push(skb, skb->data - skb_network_header(skb));
 
 	if ((skb = skb_unshare(skb, GFP_ATOMIC)) == NULL)
 		return NET_RX_DROP;
@@ -425,7 +425,7 @@
 	unsigned char tmp[ETH_ALEN];
 
 	/* Add back all headers */
-	skb_push(skb, skb->data - skb->nh.raw);
+	skb_push(skb, skb->data - skb_network_header(skb));
 
 	if ((skb = skb_unshare(skb, GFP_ATOMIC)) == NULL)
 		return NET_RX_DROP;