Fix qrfcomm unit test

The patch also aligns the error behavior of QBluetoothServer::listen()
across the various platforms.

Task-number: QTBUG-22017
Change-Id: Ic81808c94d060ca07bd125afa842452e53efaec7
Reviewed-by: Nedim Hadzic <nedimhadzija@gmail.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>