In this mode all clients get NameOwnerChanged events for all
unique names. This means you can track lifetimes of these, even if
you can't talk to them. This is useful on the a11y bus, because
we want to track when there are any listeners to a particular event,
and this is done my listing unique id:s and tracking them.
This adds a new policy level FILTERED which is betweew SEEN
and TALK. It implies all that SEEN does, but additionally lets
you send method calls to a well known name that matches a
filter which can match against interface name, member name and
object path.
Note: To make the implementation simpler, this does not grant
similar access when sending the peer messages via the unique name,
only when using the well known name does this work.
