netfilter: nf_tables: hide clash bit from userspace

Its a kernel implementation detail, at least at this time:

We can later decide to revert this patch if there is a compelling
reason, but then we should also remove the ifdef that prevents exposure
of ip_conntrack_status enum IPS_NAT_CLASH value in the uapi header.

Clash entries are not included in dumps (true for both old /proc
and ctnetlink) either.  So for now exclude the clash bit when dumping.

Fixes: 7e5c6aa6 ("netfilter: nf_tables: add packets conntrack state to debug trace info")
Link: https://lore.kernel.org/netfilter-devel/aGwf3dCggwBlRKKC@strlen.de/


Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>