pkg/fqdn: add a test for fqdn caches overlimit behaviour
pkg/fqdn: add a test for fqdn caches overlimit behaviour

Add a unit test to verify that the DNS cache GC and the DNS zombies
cache GC, in case of overlimit (i.e. too many IPs for the same host),
will select entries with earlier expiration time for eviction.

The test scenario, with lot of entries related to the same name, may
happen with a host that changes its IP very frequently. In that case, we
want to ensure that the more recent entries (i.e. entries with later
expiration time) are preferred (i.e. kept alive) while garbage
collecting the DNS caches.

Signed-off-by: Fabio Falzoi <a3958b26c18ad01cbee6627c44adab1006401257@isovalent.com>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium