[SK_BUFF]: Introduce skb_reset_mac_header(skb)

For the common, open coded 'skb->mac.raw = skb->data' operation, so that we can
later turn skb->mac.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/drivers/net/cxgb3/sge.c b/drivers/net/cxgb3/sge.c
index 8946f7a..b5cf2a6 100644
--- a/drivers/net/cxgb3/sge.c
+++ b/drivers/net/cxgb3/sge.c
@@ -1620,7 +1620,8 @@
 			     unsigned int gather_idx)
 {
 	rq->offload_pkts++;
-	skb->mac.raw = skb->nh.raw = skb->h.raw = skb->data;
+	skb_reset_mac_header(skb);
+	skb->nh.raw = skb->h.raw = skb->data;
 
 	if (rq->polling) {
 		rx_gather[gather_idx++] = skb;