code: func (n *upnpNAT) DeletePortMapping(protocol string, externalPort, internalPort int) (err error) {
  
  	message := "<u:DeletePortMapping xmlns:u=\"urn:schemas-upnp-org:service:WANIPConnection:1\">\r\n" +
  		"<NewRemoteHost></NewRemoteHost><NewExternalPort>" + strconv.Itoa(externalPort) +
  		"</NewExternalPort><NewProtocol>" + strings.ToUpper(protocol) + "</NewProtocol>" +
  		"</u:DeletePortMapping>"
  
  	response, err := soapRequest(n.serviceURL, "DeletePortMapping", message)
  	if err != nil {
  		return
  	}
  
  	// TODO: check response to see if the port was deleted
  	// log.Println(message, response)
  	_ = response
  	return
  }
docs: // DeletePortMapping implements the NAT interface by removing up a port forwarding
  // from the UPnP router to the local machine with the given ports and.