nft: Fix selective chain compatibility checks

nft: Fix selective chain compatibility checks

Since commit 80251bc2a56ed ("nft: remove cache build calls"), 'chain'
parameter passed to nft_chain_list_get() is no longer effective.
Before, it was used to fetch only that single chain from kernel when
populating the cache. So the returned list of chains for which
compatibility checks are done would contain only that single chain.

Re-establish the single chain compat checking by introducing a dedicated
code path to nft_is_chain_compatible() doing so.

Fixes: 80251bc2a56ed ("nft: remove cache build calls")
Signed-off-by: Phil Sutter <phil@nwl.cc>