[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>

net/iucv/af_iucv.c

@@ -954,7 +954,7 @@ static void iucv_callback_rx(struct iucv_path *path, struct iucv_message *msg)
 		}
 
 		skb->h.raw = skb->data;
-		skb->nh.raw = skb->data;
+		skb_reset_network_header(skb);
 		skb->len = msg->length;
 	}