Every time use permissive control in function memberof_mod.
    
    Storing cyclic groups into sysdb can cause adding ghost members,
    which has already been stored. Function ldb_modify will fail
    with error [Attribute or value exists].
    
    With permisive control, duplicated attributes will be skipped
    as if it was never added.
    
    https://fedorahosted.org/sssd/ticket/1846