[SK_BUFF]: Introduce skb_network_header_len

For the common sequence "skb->h.raw - skb->nh.raw", similar to skb->mac_len,
that is precalculated tho, don't think we need to bloat skb with one more
member, so just use this new helper, reducing the number of non-skbuff.h
references to the layer headers even more.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/pasemi_mac.c b/drivers/net/pasemi_mac.c
index 1d81299..76fe9dd 100644
--- a/drivers/net/pasemi_mac.c
+++ b/drivers/net/pasemi_mac.c
@@ -734,12 +734,12 @@
 		switch (ip_hdr(skb)->protocol) {
 		case IPPROTO_TCP:
 			dflags |= XCT_MACTX_CSUM_TCP;
-			dflags |= XCT_MACTX_IPH((skb->h.raw - skb->nh.raw) >> 2);
+			dflags |= XCT_MACTX_IPH(skb_network_header_len(skb) >> 2);
 			dflags |= XCT_MACTX_IPO(nh - skb->data);
 			break;
 		case IPPROTO_UDP:
 			dflags |= XCT_MACTX_CSUM_UDP;
-			dflags |= XCT_MACTX_IPH((skb->h.raw - skb->nh.raw) >> 2);
+			dflags |= XCT_MACTX_IPH(skb_network_header_len(skb) >> 2);
 			dflags |= XCT_MACTX_IPO(nh - skb->data);
 			break;
 		}