netfilter: conntrack: tag conntracks picked up in local out hook

This allows to identify flows that originate from local machine
in a followup patch.

It would be possible to make this a ->status bit instead.
For now I did not do that yet because I don't have a use-case for
exposing this info to userspace.

If one comes up the toggle can be replaced with a status bit.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_conntrack.h

@@ -95,6 +95,7 @@ struct nf_conn {
 	unsigned long status;
 
 	u16		cpu;
+	u16		local_origin:1;
 	possible_net_t ct_net;
 
 #if IS_ENABLED(CONFIG_NF_NAT)

net/netfilter/nf_conntrack_core.c

@@ -1747,6 +1747,9 @@ resolve_normal_ct(struct nf_conn *tmpl,
 			return 0;
 		if (IS_ERR(h))
 			return PTR_ERR(h);
+
+		ct = nf_ct_tuplehash_to_ctrack(h);
+		ct->local_origin = state->hook == NF_INET_LOCAL_OUT;
 	}
 	ct = nf_ct_tuplehash_to_ctrack(h);