daemon: Initialize dbus to use thread-safe mode by default

daemon: Initialize dbus to use thread-safe mode by default

In most cases, we use dbus from more than one thread, as we
e.g. enable real-time scheduling from the ALSA threads.
Therefore set dbus to thread-safe mode by default, as recommended
in https://bugs.freedesktop.org/show_bug.cgi?id=47060#c5

This fixes a bug where PulseAudio could crash in two parallel
calls to pa_make_realtime.

BugLink: https://bugs.launchpad.net/bugs/937933
Signed-off-by: David Henningsson <david.henningsson@canonical.com>