code: func NewInjectable(fd int, mtu uint32, capabilities stack.LinkEndpointCapabilities) (tcpip.LinkEndpointID, *InjectableEndpoint) {
  	syscall.SetNonblock(fd, true)
  
  	e := &InjectableEndpoint{endpoint: endpoint{
  		fd:   fd,
  		mtu:  mtu,
  		caps: capabilities,
  	}}
  
  	return stack.RegisterLinkEndpoint(e), e
  }
docs: // NewInjectable creates a new fd-based InjectableEndpoint.