[IP]: Introduce ip_hdrlen()

For the common sequence "skb->nh.iph->ihl * 4", removing a good number of open
coded skb->nh.iph uses, now to go after the rest...

Just out of curiosity, here are the idioms found to get the same result:

skb->nh.iph->ihl << 2
skb->nh.iph->ihl<<2
skb->nh.iph->ihl * 4
skb->nh.iph->ihl*4
(skb->nh.iph)->ihl * sizeof(u32)

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_main.c b/drivers/net/netxen/netxen_nic_main.c
index 7d2525e..b548a30 100644
--- a/drivers/net/netxen/netxen_nic_main.c
+++ b/drivers/net/netxen/netxen_nic_main.c
@@ -41,6 +41,7 @@
 
 #include <linux/dma-mapping.h>
 #include <linux/vmalloc.h>
+#include <net/ip.h>
 
 MODULE_DESCRIPTION("NetXen Multi port (1/10) Gigabit Network Driver");
 MODULE_LICENSE("GPL");
@@ -778,9 +779,8 @@
 		if (skb_shinfo(skb)->gso_size > 0) {
 
 			no_of_desc++;
-			if (((skb->nh.iph)->ihl * sizeof(u32)) +
-			    ((skb->h.th)->doff * sizeof(u32)) +
-			    sizeof(struct ethhdr) >
+			if ((ip_hdrlen(skb) + skb->h.th->doff * 4 +
+			     sizeof(struct ethhdr)) >
 			    (sizeof(struct cmd_desc_type0) - 2)) {
 				no_of_desc++;
 			}