[SK_BUFF]: Introduce skb_transport_offset()

For the quite common 'skb->h.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/net/netxen/netxen_nic_hw.c b/drivers/net/netxen/netxen_nic_hw.c
index 28d68c3..09ca219 100644
--- a/drivers/net/netxen/netxen_nic_hw.c
+++ b/drivers/net/netxen/netxen_nic_hw.c
@@ -387,7 +387,7 @@
 		}
 	}
 	adapter->stats.xmitcsummed++;
-	desc->tcp_hdr_offset = skb->h.raw - skb->data;
+	desc->tcp_hdr_offset = skb_transport_offset(skb);
 	desc->ip_hdr_offset = skb_network_offset(skb);
 }