code: func (e *endpoint) Bind(addr tcpip.FullAddress) *tcpip.Error {
  	e.mu.Lock()
  	defer e.mu.Unlock()
  
  	err := e.bindLocked(addr)
  	if err != nil {
  		return err
  	}
  
  	// Save the effective NICID generated by bindLocked.
  	e.bindNICID = e.regNICID
  
  	return nil
  }
docs: // Bind binds the endpoint to a specific local address and port.
  // Specifying a NIC is optional.