GATTS_AddCharacteristic() function

* Function GATTS_AddCharacteristic * Description This function is called to add a characteristic into a service. * It will add a characteristic declaration and characteristic * value declaration into the service database identified by the * service handle. * Parameter service_handle : To which service this included service is added to. * char_uuid : Characteristic UUID. * perm : Characteristic value declaration attribute permission. * property : Characteristic Properties * Returns Characteristic value declaration attribute handle. 0 if add * characteristic failed.