[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/ipcomp6.c

@@ -79,7 +79,7 @@ static int ipcomp6_input(struct xfrm_state *x, struct sk_buff *skb)
 	skb->ip_summed = CHECKSUM_NONE;
 
 	/* Remove ipcomp header and decompress original payload */
-	iph = skb->nh.ipv6h;
+	iph = ipv6_hdr(skb);
 	ipch = (void *)skb->data;
 	skb->h.raw = skb->nh.raw + sizeof(*ipch);
 	__skb_pull(skb, sizeof(*ipch));