Michael Baudino authored Mar 05, 2019 and OyyoDams committed May 08, 2019

This commit adds a CI stage that runs Buildroot integrated linter
(`check-package`) against all our `.mk`, `.hash` and `Config.in` files.

This new CI stage can be run locally using:

```bash
gitlab-runner exec docker "lint buildroot packages"
```

It also fixes a few codestyle offenses introduced recently (necessary
for the CI to pass).