So it won't spam ctrld log unnecessary, prevent confusion. While at it,
also change the log level from Warn to Info, since this error is not
actionable by the user.
In case the resolver could not reach nameserver, ptr discover should
only print error message once, then stop doing the query until the
nameserver is reachable. This would prevent ptr discover from flooding
ctrld log with a lot of duplicated messages.
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.
Cuong Manh Le