nat/upnp.go
func (n *upnp) DeleteMapping(protocol string, extPort, intPort int) error {
	return n.client.DeletePortMapping(
		"", uint16(extPort), strings.ToUpper(protocol))
}
func (n *upnp) DeleteMapping(protocol string, extPort, intPort int) error {
	return n.client.DeletePortMapping(
		"", uint16(extPort), strings.ToUpper(protocol))
}
// DeleteMapping removes the port mapping to UPnP interface.