nat/nat.go
func (n *discovery) DeleteMapping(protocol string, extPort, intPort int) error {
	if err := n.wait(); err != nil {
		return err
	}
	return n.found.DeleteMapping(protocol, extPort, intPort)
}
func (n *discovery) DeleteMapping(protocol string, extPort, intPort int) error {
	if err := n.wait(); err != nil {
		return err
	}
	return n.found.DeleteMapping(protocol, extPort, intPort)
}
// DeleteMapping removes the port mapping.