[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/netfilter/nf_nat_helper.c b/net/ipv4/netfilter/nf_nat_helper.c
index 49a90c3..723302a 100644
--- a/net/ipv4/netfilter/nf_nat_helper.c
+++ b/net/ipv4/netfilter/nf_nat_helper.c
@@ -190,7 +190,7 @@
 				    (int)rep_len - (int)match_len,
 				    ct, ctinfo);
 		/* Tell TCP window tracking about seq change */
-		nf_conntrack_tcp_update(*pskb, (*pskb)->nh.iph->ihl*4,
+		nf_conntrack_tcp_update(*pskb, ip_hdrlen(*pskb),
 					ct, CTINFO2DIR(ctinfo));
 	}
 	return 1;
@@ -318,8 +318,8 @@
 	unsigned int dir, optoff, optend;
 	struct nf_conn_nat *nat = nfct_nat(ct);
 
-	optoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct tcphdr);
-	optend = (*pskb)->nh.iph->ihl*4 + tcph->doff*4;
+	optoff = ip_hdrlen(*pskb) + sizeof(struct tcphdr);
+	optend = ip_hdrlen(*pskb) + tcph->doff * 4;
 
 	if (!skb_make_writable(pskb, optend))
 		return 0;
@@ -371,10 +371,10 @@
 	this_way = &nat->info.seq[dir];
 	other_way = &nat->info.seq[!dir];
 
-	if (!skb_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
+	if (!skb_make_writable(pskb, ip_hdrlen(*pskb) + sizeof(*tcph)))
 		return 0;
 
-	tcph = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
+	tcph = (void *)(*pskb)->data + ip_hdrlen(*pskb);
 	if (after(ntohl(tcph->seq), this_way->correction_pos))
 		newseq = htonl(ntohl(tcph->seq) + this_way->offset_after);
 	else
@@ -399,7 +399,7 @@
 	if (!nf_nat_sack_adjust(pskb, tcph, ct, ctinfo))
 		return 0;
 
-	nf_conntrack_tcp_update(*pskb, (*pskb)->nh.iph->ihl*4, ct, dir);
+	nf_conntrack_tcp_update(*pskb, ip_hdrlen(*pskb), ct, dir);
 
 	return 1;
 }