cache: Filter chain list on kernel side

cache: Filter chain list on kernel side

When operating on a specific chain, add payload to NFT_MSG_GETCHAIN so
kernel returns only relevant data. Since ENOENT is an expected return
code, do not treat this as error.

While being at it, improve code in chain_cache_cb() a bit:
- Check chain's family first, it is a less expensive check than
  comparing table names.
- Do not extract chain name of uninteresting chains.

Signed-off-by: Phil Sutter <phil@nwl.cc>