Fix Packet Broker audience from dial address

[johanstokking]

Summary

References https://github.com/TheThingsIndustries/lorawan-stack-support/issues/972

Changes

This fixes the issue that the token audience is not correctly parsed from the address to dial.

Testing

Unit test

Regressions

None expected

Notes for Reviewers

This is the least ugly version that I considered.

I didn't update the changelog yet because we need to decide if we backport this to 3.26.

Let's get this in for 3.26.2.

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.
• 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.