[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/esp6.c b/net/ipv6/esp6.c
index 363e63f..6e6b57a 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -92,8 +92,8 @@
 	top_iph = (struct ipv6hdr *)__skb_push(skb, hdr_len);
 	esph = (struct ipv6_esp_hdr *)skb->h.raw;
 	top_iph->payload_len = htons(skb->len + alen - sizeof(*top_iph));
-	*(u8*)(trailer->tail - 1) = *skb->nh.raw;
-	*skb->nh.raw = IPPROTO_ESP;
+	*(u8 *)(trailer->tail - 1) = *skb_network_header(skb);
+	*skb_network_header(skb) = IPPROTO_ESP;
 
 	esph->spi = x->id.spi;
 	esph->seq_no = htonl(++x->replay.oseq);