AVRC_UnitCmd() function

* Function AVRC_UnitCmd * Description Send a UNIT INFO command to the peer device. This * function can only be called for controller role connections. * Any response message from the peer is passed back through * the tAVRC_MSG_CBACK callback function. * Input Parameters: * handle: Handle of this connection. * label: Transaction label. * Output Parameters: * None. * Returns AVRC_SUCCESS if successful. * AVRC_BAD_HANDLE if handle is invalid.