[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/s390/net/qeth_main.c b/drivers/s390/net/qeth_main.c
index d502b77..2882202 100644
--- a/drivers/s390/net/qeth_main.c
+++ b/drivers/s390/net/qeth_main.c
@@ -2278,7 +2278,7 @@
 	    (card->info.link_type == QETH_LINK_TYPE_LANE_TR))
 	 	return tr_type_trans(skb,dev);
 #endif /* CONFIG_TR */
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 	skb_pull(skb, ETH_HLEN );
 	eth = eth_hdr(skb);
 
@@ -2461,7 +2461,7 @@
 	if (card->options.fake_ll)
 		qeth_rebuild_skb_fake_ll(card, skb, hdr);
 	else
-		skb->mac.raw = skb->data;
+		skb_reset_mac_header(skb);
 	skb->ip_summed = card->options.checksum_type;
 	if (card->options.checksum_type == HW_CHECKSUMMING){
 		if ( (hdr->hdr.l3.ext_flags &