code: func New(lower tcpip.LinkEndpointID) (tcpip.LinkEndpointID, *Endpoint) {
  	e := &Endpoint{
  		lower: stack.FindLinkEndpoint(lower),
  	}
  	return stack.RegisterLinkEndpoint(e), e
  }
docs: // New creates a new waitable link-layer endpoint. It wraps around another
  // endpoint and allows the caller to block new write/dispatch calls and wait for
  // the inflight ones to finish before returning.