PROXY: Use right name in ldap filter
    
    We used internal fq name in ldap filter
    with id_provider proxy to files and auth provider
    ldap
    
    [sssd[be[LDAP]]] [sdap_get_generic_ext_step]
        (0x0400): calling ldap_search_ext with
        [(&(uid=testuser1@ldap)(objectclass=posixAccount))][dc=example,dc=com].
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>