docs: def set_tunnel(self, tunnel_type, tunnel, callback=None):
          """
          set_tunnel(self, tunnel_type, tunnel, callback=None):
          """
          orig_tunnel = self.tunnels.get(tunnel_type, (None, None))[0]
          if orig_tunnel is not None:
              _logger.debug("Unsubscribe: %s", (orig_tunnel,))
              self.client.unsubscribe(str(orig_tunnel))
  
          self.tunnels[tunnel_type] = (tunnel, callback)
  
          if callback is not None:
              self.message_callback_add(tunnel, callback)
  
          self.client.subscribe(str(tunnel))
          _logger.debug("Subscribe: %s", (tunnel,))