[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/ipv4/esp4.c b/net/ipv4/esp4.c
index 3104112..222d21e 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -57,9 +57,10 @@
 	*(u8*)(trailer->tail + clen-skb->len - 2) = (clen - skb->len)-2;
 	pskb_put(skb, trailer, clen - skb->len);
 
-	__skb_push(skb, skb->data - skb->nh.raw);
+	__skb_push(skb, skb->data - skb_network_header(skb));
 	top_iph = skb->nh.iph;
-	esph = (struct ip_esp_hdr *)(skb->nh.raw + top_iph->ihl*4);
+	esph = (struct ip_esp_hdr *)(skb_network_header(skb) +
+				     top_iph->ihl * 4);
 	top_iph->tot_len = htons(skb->len + alen);
 	*(u8*)(trailer->tail - 1) = top_iph->protocol;
 
@@ -222,7 +223,7 @@
 
 	if (x->encap) {
 		struct xfrm_encap_tmpl *encap = x->encap;
-		struct udphdr *uh = (void *)(skb->nh.raw + ihl);
+		struct udphdr *uh = (void *)(skb_network_header(skb) + ihl);
 
 		/*
 		 * 1) if the NAT-T peer's IP or port changed then