[SK_BUFF]: Introduce skb_network_header()

For the places where we need a pointer to the network header, it is still legal
to touch skb->nh.raw directly if just adding to, subtracting from or setting it
to another layer header.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index aa4a0a5..e5293b3 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -284,7 +284,8 @@
 	if (opt->dsthao) {
 		off = ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO);
 		if (likely(off >= 0)) {
-			hao = (struct ipv6_destopt_hao *)(skb->nh.raw + off);
+			hao = (struct ipv6_destopt_hao *)
+					(skb_network_header(skb) + off);
 			ipv6_addr_copy(&tmp, &iph->saddr);
 			ipv6_addr_copy(&iph->saddr, &hao->addr);
 			ipv6_addr_copy(&hao->addr, &tmp);