[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/irda-usb.c b/drivers/net/irda/irda-usb.c
index 1d510bd..6ef375a 100644
--- a/drivers/net/irda/irda-usb.c
+++ b/drivers/net/irda/irda-usb.c
@@ -921,7 +921,7 @@
 
 	/* Ask the networking layer to queue the packet for the IrDA stack */
 	dataskb->dev = self->netdev;
-	dataskb->mac.raw  = dataskb->data;
+	skb_reset_mac_header(dataskb);
 	dataskb->protocol = htons(ETH_P_IRDA);
 	len = dataskb->len;
 	netif_rx(dataskb);