Make it possible to compile with tcp tracing again

[karknu]

Description

The correct define is linux_HOST_OS. For some reason it was changed in a refactoring.

Checklist

Quality

• [x] Commit sequence makes sense and have useful messages, see ref.
• [ ] New tests are added and existing tests are updated.
• [ ] Self-reviewed the PR.

Maintenance

• [ ] Linked an issue or added the PR to the current sprint of ouroboros-network project.
• [ ] Added labels.
• [ ] Updated changelog files.
• [ ] The documentation has been properly updated, see ref.