[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/airo.c b/drivers/net/wireless/airo.c
index e50b148..692a23f 100644
--- a/drivers/net/wireless/airo.c
+++ b/drivers/net/wireless/airo.c
@@ -3411,7 +3411,7 @@
 			OUT4500( apriv, EVACK, EV_RX);
 
 			if (test_bit(FLAG_802_11, &apriv->flags)) {
-				skb->mac.raw = skb->data;
+				skb_reset_mac_header(skb);
 				skb->pkt_type = PACKET_OTHERHOST;
 				skb->dev = apriv->wifidev;
 				skb->protocol = htons(ETH_P_802_2);
@@ -3746,7 +3746,7 @@
 		wireless_spy_update(ai->dev, sa, &wstats);
 	}
 #endif /* IW_WIRELESS_SPY */
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 	skb->pkt_type = PACKET_OTHERHOST;
 	skb->dev = ai->wifidev;
 	skb->protocol = htons(ETH_P_802_2);