code: func (s *Stack) AddTCPProbe(probe TCPProbeFunc) {
  	s.mu.Lock()
  	s.tcpProbeFunc = probe
  	s.mu.Unlock()
  }
docs: // AddTCPProbe installs a probe function that will be invoked on every segment
  // received by a given TCP endpoint. The probe function is passed a copy of the
  // TCP endpoint state.
  //
  // NOTE: TCPProbe is added only to endpoints created after this call. Endpoints
  // created prior to this call will not call the probe function.
  //
  // Further, installing two different probes back to back can result in some
  // endpoints calling the first one and some the second one. There is no
  // guarantee provided on which probe will be invoked. Ideally this should only
  // be called once per stack.