LDAP: Fix nesting level comparison
Correct an issue with nesting level comparison of option
ldap_group_nesting_level to ensure that setting nesting level 0
will avoid parent group of group searches.
Resolves:
https://pagure.io/SSSD/sssd/issue/3425
Reviewed-by: Fabiano FidĂȘncio <fidencio@redhat.com>