[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/irda/w83977af_ir.c b/drivers/net/irda/w83977af_ir.c
index 4212657..bee4451 100644
--- a/drivers/net/irda/w83977af_ir.c
+++ b/drivers/net/irda/w83977af_ir.c
@@ -919,7 +919,7 @@
 			self->stats.rx_packets++;
 			
 			skb->dev = self->netdev;
-			skb->mac.raw  = skb->data;
+			skb_reset_mac_header(skb);
 			skb->protocol = htons(ETH_P_IRDA);
 			netif_rx(skb);
 			self->netdev->last_rx = jiffies;