Unbound: allow configuring cache-max-negative-ttl

[feld]

Dropping the negative cache TTL as low as possible is really useful.

e.g., I try to resolve a host that's been offline for a while, then boot up the machine. It gets an IP from DHCP, sets its hostname, and now Unbound should know about it. But it doesn't return any results because there's a negative cache entry still there.

[CJ]

Interesting.  I don't think that's situation I've typically come across.

My local hosts that don't have a DHCP record don't seem to get cached, despite my setting the default to 900s.  Online records are respecting my min of 900s, though.  Maybe it's using a different TTL for LAN vs WAN?