[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>

net/bluetooth/bnep/core.c

@@ -326,7 +326,7 @@ static inline int bnep_rx_frame(struct bnep_session *s, struct sk_buff *skb)
 		return 0;
 	}
 
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 
 	/* Verify and pull out header */
 	if (!skb_pull(skb, __bnep_rx_hlen[type & BNEP_TYPE_MASK]))