[SK_BUFF]: Introduce skb_reset_network_header(skb)

For the common, open coded 'skb->nh.raw = skb->data' operation, so that we can
later turn skb->nh.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/hamradio/bpqether.c b/drivers/net/hamradio/bpqether.c
index d254269..656f278 100644
--- a/drivers/net/hamradio/bpqether.c
+++ b/drivers/net/hamradio/bpqether.c
@@ -282,7 +282,7 @@
 	}
 
 	skb->protocol = ax25_type_trans(skb, dev);
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 	dev->hard_header(skb, dev, ETH_P_BPQ, bpq->dest_addr, NULL, 0);
 	bpq->stats.tx_packets++;
 	bpq->stats.tx_bytes+=skb->len;