Otherwise, this file would need to be included in POTFILES.in.
This is unnecessary.

Fixes: 06cf1f5e2d3e ('platform/tests: extend monitor tool to dump the state of NMPlatform')

Unfortunately, for this we require SetLinkDNSEx() API from v246.
That adds extra complexity.

If the configuration contains no server name, we continue using
SetLinkDNS(). Otherwise, at first we try using SetLinkDNSEx().
We will notice if that method is unsupported, reconfigure with
SetLinkDNS(), and set a flag to not try that again.

- rename the "has_" variables to have the same name as the API that they
  check.
- do an if-else-if for checking the operation when detecting support.

This just feels nicer. No strong reasons.

The DNS name can now also contain the DoT server name. It's not longer a
binary IP address only.

Extend NML3ConfigData to account for that. To track the additional
data, use the string representation. The alternative to have a separate
type that contains the parsed information would be cumbersome too.

It is almost always wrong, to split IPv4 and IPv6 behaviors at a high level.
Most of the code does something very similar. Combine the two functions.
and let them handle the difference closer to where it is.

The double negation is hard to understand.

Instead of assuming any address that disappeared was because of a DAD
failure, check explicitly that either:

 - the address is still present with DADFAILED flag (in case it was a
   permanent address), or

 - the address was removed and platform recorded that it had the
   DADFAILED flag.

A DAD failure is in most cases a symptom of a network
misconfiguration; as such it must be logged in the default
configuration (info level).

While at it, fix other log messages.