[SK_BUFF]: Introduce ipv6_hdr(), remove skb->nh.ipv6h

Now the skb->nh union has just one member, .raw, i.e. it is just like the
skb->mac union, strange, no? I'm just leaving it like that till the transport
layer is done with, when we'll rename skb->mac.raw to skb->mac_header (or
->mac_header_offset?), ditto for ->{h,nh}.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/xfrm6_input.c

@@ -35,7 +35,7 @@ int xfrm6_rcv_spi(struct sk_buff *skb, __be32 spi)
 		goto drop;
 
 	do {
-		struct ipv6hdr *iph = skb->nh.ipv6h;
+		struct ipv6hdr *iph = ipv6_hdr(skb);
 
 		if (xfrm_nr == XFRM_MAX_DEPTH)
 			goto drop;
@@ -112,7 +112,7 @@ int xfrm6_rcv_spi(struct sk_buff *skb, __be32 spi)
 		return -1;
 	} else {
 #ifdef CONFIG_NETFILTER
-		skb->nh.ipv6h->payload_len = htons(skb->len);
+		ipv6_hdr(skb)->payload_len = htons(skb->len);
 		__skb_push(skb, skb->data - skb_network_header(skb));
 
 		NF_HOOK(PF_INET6, NF_IP6_PRE_ROUTING, skb, skb->dev, NULL,