Disconnect gateway on Gateway Server address change

[adriansmares]

Summary

References https://github.com/TheThingsIndustries/lorawan-stack-support/issues/1007

Changes

• Disconnect gateways if the Gateway Server address has changed.

Testing

Local testing. Manual testing steps:

1. Register a Basic Station gateway. You may use LNS directly or do it via CUPS.
2. Connect the gateway.
3. After the gateway has connected, change the gateway server address.
4. You will have to wait approximately 12 minutes for the periodic check to occur.
5. Your gateway should disconnect with error gateway_changed.

Regressions

N/A. The gateway server address is covered by the already existing API key rights, so there shouldn't be any regression.

Notes for Reviewers

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• The steps/process to test this feature are clearly explained including testing for regressions.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.