docs: def _get_server_cls(self, host):
          """Return an appropriate WSGI server class base on provided host
          :param host: The listen host for the zaqar API server.
          """
          server_cls = simple_server.WSGIServer
          if netutils.is_valid_ipv6(host):
              if getattr(server_cls, 'address_family') == socket.AF_INET:
                  class server_cls(server_cls):
                      address_family = socket.AF_INET6
          return server_cls