add timeout handler

[zey1996]

I believe that developers should have a way to know when a data packet is lost or does not return within a specified time.

you can set MaxRtt and OnTimeout func

Ontime func while be call when a request was not answered within a specified time

you only need add:

  pinger.MaxRtt = time.Second * 3

  pinger.OnTimeOut = func(packet *probing.Packet) {
    fmt.Println("timeout", packet.Addr, packet.Rtt, packet.TTL)
  }

It has good compatibility, as if MaxRtt is not set, it will have the same behavior as before.

However, there are still some issues remaining.

• The timing is not precise; for example, if a maximum round-trip time (maxrtt) of 100ms is set, but the request time exceeds 101ms, it is possible that the OnRecv function will still be used.
• If a request is received after the timeout, the OnDuplicateRecv function will be called.

But I believe that this is acceptable.

[SuperQ]

This needs a DCO sign-off. You can use git commit -s --amend to add it.

[zey1996]

please see also: https://github.com/prometheus-community/pro-bing/pull/49