- Fix cache update when serve expired is used in order to not evict
still usable expired records. Modules are forbidden to update the
cache if their answer is DNSSEC unchecked or bogus and a valid
(expired) entry already exists. Bogus replies from the validator are
also discarded in favor of existing (expired) valid replies.
- serve-expired-ttl-reset should try to keep expired records in the
cache in case they are reset.
