Bug#882504: Problem still exists

I can confirm that adding RequiredForOnline=no to the unconfigured interface's .network file resolves the timeout issue.

I did want to ask about the broader user experience: "apt-helper wait-online" calls "systemd-networkd-wait-online"
without any interface arguments, which means it waits for all interfaces systemd-networkd manages. For users with
unconfigured interfaces (secondary ethernet, unused wifi cards on servers, etc.), this causes a 30-second delay on every
apt-daily run.

While the RequiredForOnline=no solution works, it requires users to know about this systemd-networkd option and manually
create .network files. Would it be worth considering one of the following?

* A configuration option in apt to specify which interfaces to wait for
* Documenting this behavior more prominently in apt's documentation?

The current behavior was surprising to me, since I had expected apt to work without manual systemd-networkd
configuration.