[IPSEC]: Fix pure tunnel modes involving IPv6

I noticed that my recent patch broke 6-on-4 pure IPsec tunnels (the ones
that are only used for incompressible IPsec packets).  Subsequent reviews
show that I broke 6-on-6 pure tunnels more than three years ago and nobody
ever noticed. I suppose every must be testing 6-on-6 IPComp with large
pings which are very compressible :)

This patch fixes both cases.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/xfrm4_tunnel.c

@@ -18,7 +18,7 @@ static int ipip_output(struct xfrm_state *x, struct sk_buff *skb)
 
 static int ipip_xfrm_rcv(struct xfrm_state *x, struct sk_buff *skb)
 {
-	return IPPROTO_IP;
+	return ip_hdr(skb)->protocol;
 }
 
 static int ipip_init_state(struct xfrm_state *x)

net/ipv6/xfrm6_tunnel.c

@@ -248,7 +248,7 @@ static int xfrm6_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
 
 static int xfrm6_tunnel_input(struct xfrm_state *x, struct sk_buff *skb)
 {
-	return 0;
+	return skb_network_header(skb)[IP6CB(skb)->nhoff];
 }
 
 static int xfrm6_tunnel_rcv(struct sk_buff *skb)