[SK_BUFF]: Introduce skb_network_offset()

For the quite common 'skb->nh.raw - skb->data' sequence.

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 fadb9291..0c2b375 100644
--- a/drivers/isdn/i4l/isdn_net.c
+++ b/drivers/isdn/i4l/isdn_net.c
@@ -1121,7 +1121,7 @@
 	if (!skb)
 		return;
 	if (lp->p_encap == ISDN_NET_ENCAP_ETHER) {
-		int pullsize = (ulong)skb->nh.raw - (ulong)skb->data - ETH_HLEN;
+		const int pullsize = skb_network_offset(skb) - ETH_HLEN;
 		if (pullsize > 0) {
 			printk(KERN_DEBUG "isdn_net: Pull junk %d\n", pullsize);
 			skb_pull(skb, pullsize);