[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/wireless/orinoco.c b/drivers/net/wireless/orinoco.c
index 3f9d78d..f1415bf 100644
--- a/drivers/net/wireless/orinoco.c
+++ b/drivers/net/wireless/orinoco.c
@@ -770,7 +770,7 @@
 
 	/* Copy the 802.11 header to the skb */
 	memcpy(skb_put(skb, hdrlen), &(desc->frame_ctl), hdrlen);
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 
 	/* If any, copy the data from the card to the skb */
 	if (datalen > 0) {