Once resource record (RR) was used to extract necessary information, it
should be freed in memory. However, the current way that ctrld declare
the RRs causing the slices to be heap allocated, and stay in memory
longer than necessary. On system with low capacity, or firmware that GC
does not run agressively, it may causes the system memory exhausted.
To fix it, prevent RRs to be heap allocated, so they could be freed
immediately after each iterations.
If we see permission denied error when probing dns, that mean the
current ctrld process won't be able to do that anyway. So the probing
loop must be terminated to prevent waste of resources, or false positive
from system firewall because of too many failed attempts.
When avahi-daemon is avaibale, reading data from its cache help ctrld
populate the mdns data with already known services within local network,
allowing discover client info more quickly.
So ctrld can record the raw/original client IP instead of looking up
from MAC to IP, which may not the right choice in some network setup
like using wireguard/vpn on Merlin router.
