[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/isdn/i4l/isdn_net.c b/drivers/isdn/i4l/isdn_net.c
index 838b373..fadb929 100644
--- a/drivers/isdn/i4l/isdn_net.c
+++ b/drivers/isdn/i4l/isdn_net.c
@@ -1366,7 +1366,7 @@
 	struct ethhdr *eth;
 	unsigned char *rawp;
 
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 	skb_pull(skb, ETH_HLEN);
 	eth = eth_hdr(skb);
 
@@ -1786,7 +1786,7 @@
 	}
 	skb->dev = ndev;
 	skb->pkt_type = PACKET_HOST;
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 #ifdef ISDN_DEBUG_NET_DUMP
 	isdn_dumppkt("R:", skb->data, skb->len, 40);
 #endif