All our bus calls validate whether the specified device is a loopback
device anyway on the server side. Let's hence simplify the client,
there's no value in optimizing error paths after all. But there is value
in simpler code.
This makes `resolvectl` use the verb style command line, e.g.,
`resolvectl status` or `resolvectl tlsa tcp fedoraproject.org:443`.
For compatibility, if the invocation name is `systemd-resolve`,
then it accepts the old syntax, e.g. `systemd-resolve --status`.
