GATTS_AddCharDescriptor() function

* Function GATTS_AddCharDescriptor * Description This function is called to add a characteristic descriptor * into a service database. Add descriptor should follow add char * to which it belongs, and next add char should be done only * after all add descriptors for the previous char. * Parameter service_handle : To which service this characteristic descriptor * is added to. * perm : Characteristic value declaration attribute * permission. * p_descr_uuid : Characteristic descriptor UUID. * Returns Characteristic descriptor attribute handle. 0 if add * characteristic descriptor failed.