[SK_BUFF]: Introduce skb_reset_network_header(skb)

For the common, open coded 'skb->nh.raw = skb->data' operation, so that we can
later turn skb->nh.raw into a offset, reducing the size of struct sk_buff in
64bit land while possibly keeping it as a pointer on 32bit.

This one touches just the most simple case, next will handle the slightly more
"complex" cases.

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_neigh.c b/net/decnet/dn_neigh.c
index bf701cf..4bf066c 100644
--- a/net/decnet/dn_neigh.c
+++ b/net/decnet/dn_neigh.c
@@ -261,7 +261,7 @@
 	lp->s_class  = 0;
 	lp->pt       = 0;
 
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 
 	return NF_HOOK(PF_DECnet, NF_DN_POST_ROUTING, skb, NULL, neigh->dev, dn_neigh_output_packet);
 }
@@ -300,7 +300,7 @@
 	sp->srcnode    = cb->src;
 	sp->forward    = cb->hops & 0x3f;
 
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 
 	return NF_HOOK(PF_DECnet, NF_DN_POST_ROUTING, skb, NULL, neigh->dev, dn_neigh_output_packet);
 }
@@ -342,7 +342,7 @@
 	sp->srcnode  = cb->src & dn_htons(0x03ff);
 	sp->forward  = cb->hops & 0x3f;
 
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 
 	return NF_HOOK(PF_DECnet, NF_DN_POST_ROUTING, skb, NULL, neigh->dev, dn_neigh_output_packet);
 }