[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>

net/ipv6/raw.c

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 0e2b56c..bb049f1 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -513,7 +513,7 @@
 			if (csum_skb)
 				continue;
 
-			len = skb->len - (skb->h.raw - skb->data);
+			len = skb->len - skb_transport_offset(skb);
 			if (offset >= len) {
 				offset -= len;
 				continue;
@@ -525,7 +525,7 @@
 		skb = csum_skb;
 	}
 
-	offset += skb->h.raw - skb->data;
+	offset += skb_transport_offset(skb);
 	if (skb_copy_bits(skb, offset, &csum, 2))
 		BUG();