Commit 4c7fa8df ("core: drop root requirement for
load_connection(s)/set_logging D-Bus calls") removed the enforcing of
permission in the daemon for such methods since the D-Bus daemon
configuration already does that. That change also allows clients to
send a request and not wait for a response, since we don't have to
check the caller credentials in the daemon.

In the future we might switch to polkit for these methods, breaking
clients that don't wait for a reponse, so it seems better to prevent
from beginning such behavior.

Fixes: 4c7fa8df
(cherry picked from commit dd27b79c)