netfilter: nf_tables: fix ct untracked match breakage

"ct untracked" no longer works properly due to erroneous NFT_BREAK.
We have to check ctinfo enum first.

Fixes: d9e78914

 ("netfilter: nf_tables: avoid retpoline overhead for some ct expression calls")
Reported-by: Rvfg <i@rvf6.com>
Link: https://marc.info/?l=netfilter&m=168294996212038&w=2
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>