code: func JoinOptionPriority(ep Endpoint, prio int) EndpointOption {
  	return func(ep *endpoint) {
  		// ep lock already acquired
  		c := ep.network.getController()
  		c.Lock()
  		sb, ok := c.sandboxes[ep.sandboxID]
  		c.Unlock()
  		if !ok {
  			logrus.Errorf("Could not set endpoint priority value during Join to endpoint %s: No sandbox id present in endpoint", ep.id)
  			return
  		}
  		sb.epPriority[ep.id] = prio
  	}
  }
docs: // JoinOptionPriority function returns an option setter for priority option to
  // be passed to the endpoint.Join() method.