[TCP]: Introduce tcp_hdrlen() and tcp_optlen()

The ip_hdrlen() buddy, created to reduce the number of skb->h.th-> uses and to
avoid the longer, open coded equivalent.

Ditched a no-op in bnx2 in the process.

I wonder if we should have a BUG_ON(skb->h.th->doff < 5) in tcp_optlen()...

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c
index a35f2f2..fd291fc 100644
--- a/drivers/net/sky2.c
+++ b/drivers/net/sky2.c
@@ -1392,7 +1392,7 @@
 	/* Check for TCP Segmentation Offload */
 	mss = skb_shinfo(skb)->gso_size;
 	if (mss != 0) {
-		mss += ((skb->h.th->doff - 5) * 4);	/* TCP options */
+		mss += tcp_optlen(skb); /* TCP options */
 		mss += ip_hdrlen(skb) + sizeof(struct tcphdr);
 		mss += ETH_HLEN;