[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/econet/af_econet.c b/net/econet/af_econet.c
index 487f879..099543f 100644
--- a/net/econet/af_econet.c
+++ b/net/econet/af_econet.c
@@ -345,7 +345,7 @@
 			goto out_unlock;
 
 		skb_reserve(skb, LL_RESERVED_SPACE(dev));
-		skb->nh.raw = skb->data;
+		skb_reset_network_header(skb);
 
 		eb = (struct ec_cb *)&skb->cb;