Reject second AVRCP connection.

This change rejects the RC connection from
second device if the DUT is already connected
to RC of first device.
This addresses the problem of improper closure
of Uinput device on disconnection of Avrcp
to make sure Avrcp passthrough commands work
as desired.

Change-Id: If2e39cd90575baffd0e4442b8e7cd2a91eebdf56