Every (failed) attempt to D-Bus activate a service results in log-messages
from dbus-daemon. It must be avoided to spam the logs that way.

Let connectivity check not only ask whether systemd-resolved is enabled
(and NetworkManager would like to push information there), but also
whether it looks like the service is actually available. That is,
either it has a name-owner or it's not blocked from starting.

The previous workaround was to configure main.systemd-resolved=no
in NetworkManager.conf. But that requires explict configuration.