Ticket 49257 - Reject nsslapd-cachememsize & nsslapd-cachesize when nsslapd-cache-autosize is set
    
    Description:  We need to also reject entry cache changes when cache autosizing is being used.
    
                  I also found out that we were not registering the ldbm instance callbacks at startup.
                  So all those functions were only used when creating an instance, and not after it was
                  started.
    
    https://pagure.io/389-ds-base/issue/49257
    
    Reviewed by: tbordaz(Thanks!)