MAN: Clarify the ldap_access_filter option further
    
    https://fedorahosted.org/sssd/ticket/2235
    
    The memberof example was misleading and was making aministrators think
    that the ldap_access_filter can resolve nested group memberships.
    
    Reviewed-by: Sumit Bose <sbose@redhat.com>
    Reviewed-by: Stephen Gallagher <sgallagh@redhat.com>