bus: fix installing DRIVER matches on kdbus

bus: fix installing DRIVER matches on kdbus

In kdbus we still have to support org.freedesktop.DBus matches even though
there is no real bus driver. The reason is that bus-control.c turns
NameOwnerChanged matches into proper kdbus matches. If we drop DRIVER
matches early, we will never match on name-changes for kdbus.

Two ways to fix this:

 1) Install DRIVER matches on kdbus (which is the simple way our and which
    is what this patch does).

 2) Properly fix the scope-detection to let NameOwnerChanged matches
    through (or better: block anything with Member!=NameOwnerChanged).