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.

通过使用 Docker 占用端口 9100、从 VS Code 启动 Flutter 应用，并使用 lsof 或 curl 检查监听器来复现该问题。将配置的 dart.devToolsPort 值 10999 与 9100 上额外的 DevTools 监听器进行比较；当 DevTools 使用预期端口且不影响 Docker 服务时，即表示完成。

由索引模型根据 Issue 内容生成。