DevTools bind to already used port

When I start a flutter app while I am already running a docker container with binding to port 9100, the flutter devtools take over that port.

OS: MacOS 11.2.3
Docker: Docker Desktop 3.2.2.

```bash
$ flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.0.3, on macOS 11.2.3 20D91 darwin-x64, locale de-DE)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.1)
[✓] VS Code (version 1.54.3)
[✓] Connected device (2 available)
! Device emulator-5554 is offline.

• No issues found!
```

Before running my flutter app:
```bash
$ sudo lsof -i :9100
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
com.docke 1388 florianbauer 121u IPv6 0xc1e172b3ec4f6581 0t0 TCP *:hp-pdl-datastr (LISTEN)
```

After running my flutter app:
```bash
$ sudo lsof -i :9100
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
com.docke 1388 florianbauer 121u IPv6 0xc1e172b3ec4f6581 0t0 TCP *:hp-pdl-datastr (LISTEN)
dart 17171 florianbauer 9u IPv4 0xc1e172b3f0526121 0t0 TCP localhost:hp-pdl-datastr (LISTEN)
dart 17171 florianbauer 10u IPv6 0xc1e172b3ec4f5f21 0t0 TCP localhost:hp-pdl-datastr (LISTEN)
```

The result of this is, that I cannot connect to my docker service anymore, until I stop the dart process.

Addition:
I am starting the Flutter app from VSCode and inside the settings.json of VSCode I placed this:
```json
{
"dart.devToolsPort": 10999
}
```
When I am opening the devtools from VSCode in Chrome the browser opens on 127.0.0.1:10999, which is correct. But still there is also a dart process binding to port 9100. When I run `curl 127.0.0.1:9100` I can see that there are also devtools running.

This behavior started after I updated to Flutter 2.0.3. And two colleagues, that work on the same project, just experienced this issue as well.

Riproduci il problema occupando la porta 9100 con Docker, avviando l’app Flutter da VS Code e controllando i listener con lsof o curl. Confronta il valore configurato di dart.devToolsPort, 10999, con il listener aggiuntivo di DevTools sulla porta 9100; il lavoro è completato quando DevTools usa la porta prevista senza interrompere il servizio Docker.

Scritto dal modello di indicizzazione a partire dal testo della issue.