[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/net/ipv4/ipvs/ip_vs_proto_tcp.c b/net/ipv4/ipvs/ip_vs_proto_tcp.c
index 16a9ebe..e65382d 100644
--- a/net/ipv4/ipvs/ip_vs_proto_tcp.c
+++ b/net/ipv4/ipvs/ip_vs_proto_tcp.c
@@ -76,8 +76,7 @@
 	struct ip_vs_service *svc;
 	struct tcphdr _tcph, *th;
 
-	th = skb_header_pointer(skb, skb->nh.iph->ihl*4,
-				sizeof(_tcph), &_tcph);
+	th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
 	if (th == NULL) {
 		*verdict = NF_DROP;
 		return 0;
@@ -127,7 +126,7 @@
 		 struct ip_vs_protocol *pp, struct ip_vs_conn *cp)
 {
 	struct tcphdr *tcph;
-	unsigned int tcphoff = (*pskb)->nh.iph->ihl * 4;
+	const unsigned int tcphoff = ip_hdrlen(*pskb);
 
 	/* csum_check requires unshared skb */
 	if (!ip_vs_make_skb_writable(pskb, tcphoff+sizeof(*tcph)))
@@ -175,7 +174,7 @@
 		 struct ip_vs_protocol *pp, struct ip_vs_conn *cp)
 {
 	struct tcphdr *tcph;
-	unsigned int tcphoff = (*pskb)->nh.iph->ihl * 4;
+	const unsigned int tcphoff = ip_hdrlen(*pskb);
 
 	/* csum_check requires unshared skb */
 	if (!ip_vs_make_skb_writable(pskb, tcphoff+sizeof(*tcph)))
@@ -224,7 +223,7 @@
 static int
 tcp_csum_check(struct sk_buff *skb, struct ip_vs_protocol *pp)
 {
-	unsigned int tcphoff = skb->nh.iph->ihl*4;
+	const unsigned int tcphoff = ip_hdrlen(skb);
 
 	switch (skb->ip_summed) {
 	case CHECKSUM_NONE:
@@ -467,8 +466,7 @@
 {
 	struct tcphdr _tcph, *th;
 
-	th = skb_header_pointer(skb, skb->nh.iph->ihl*4,
-				sizeof(_tcph), &_tcph);
+	th = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_tcph), &_tcph);
 	if (th == NULL)
 		return 0;