The policy scripts can handle now client nodes that want to be linked with other
client nodes. This is needed for nodes created by the Pulse Audio Volume Control
to monitor audio comming from other application client nodes.
These don't make much sense here. In the endpoint policy we want
the clients to be linked to the endpoint that matches their role
and never move.
Also, endpoint priorities are useless. If no endpoint matches the
role, then just ignore the client.
