[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/xfrm4_mode_beet.c b/net/ipv4/xfrm4_mode_beet.c
index eaaf356..505fca0 100644
--- a/net/ipv4/xfrm4_mode_beet.c
+++ b/net/ipv4/xfrm4_mode_beet.c
@@ -98,7 +98,7 @@
 	}
 
 	skb->nh.raw = skb->data + (phlen - sizeof(*iph));
-	memmove(skb->nh.raw, iph, sizeof(*iph));
+	memmove(skb_network_header(skb), iph, sizeof(*iph));
 	skb->h.raw = skb->data + (phlen + optlen);
 	skb->data = skb->h.raw;
 
@@ -112,7 +112,7 @@
 	else
 		iph->protocol = protocol;
 	iph->check = 0;
-	iph->check = ip_fast_csum(skb->nh.raw, iph->ihl);
+	iph->check = ip_fast_csum(skb_network_header(skb), iph->ihl);
 	err = 0;
 out:
 	return err;