Handle interrupted tests (server)

When a test is accidentally interrupted, e.g.

- unplugging client cable
- client disassociating from Wi-Fi
- `kill -9` the client,

server will stuck in previous test and no longer handles new connections indefinitely.

and client always error:
```
iperf3: error - the server is busy running a test. try again later
```

Is it possible to handle this situation, Without manually kill the server and relaunch?

Tried but failed:

- `--rcv-timeout 15000` and/or `--snd-timeout 15000`
- `--idle-timeout 15`