netfilter: nft_compat: validate chain type in match/target

We have to validate the real chain type to ensure that matches/targets
are not used out from their scope (eg. MASQUERADE in nat chain type).
The existing validation relies on the table name, but this is not
sufficient since userspace can fool us by using the appropriate table
name with a different chain type.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>