netfilter: nft_ct: reject direction for ct id

[ Upstream commit 38ed1c70 ]

Direction attribute is ignored, reject it in case this ever needs to be
supported

Fixes: 3087c3f7 ("netfilter: nft_ct: Add ct id support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>