[NETFILTER]: Fix xfrm lookup in ip_route_me_harder/ip6_route_me_harder

ip_route_me_harder doesn't use the port numbers of the xfrm lookup and
uses ip_route_input for non-local addresses which doesn't do a xfrm
lookup, ip6_route_me_harder doesn't do a xfrm lookup at all.

Use xfrm_decode_session and do the lookup manually, make sure both
only do the lookup if the packet hasn't been transformed already.

Makeing sure the lookup only happens once needs a new field in the
IP6CB, which exceeds the size of skb->cb. The size of skb->cb is
increased to 48b. Apparently the IPv6 mobile extensions need some
more room anyway.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ip.h b/include/net/ip.h
index 52f4d9c..a494d04 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -39,7 +39,8 @@
 
 #define IPSKB_FORWARDED		1
 #define IPSKB_XFRM_TUNNEL_SIZE	2
-#define IPSKB_FRAG_COMPLETE	4
+#define IPSKB_XFRM_TRANSFORMED	4
+#define IPSKB_FRAG_COMPLETE	8
 };
 
 struct ipcm_cookie