Verify that bridge vlan separation works properly for broadcast packets

[axkar]

• Verify that broadcast packets are also properly moved accross the bridge, i.e. the broadcast packets sent from vlan interface VLAN10 do not reach VLAN20

Checklist

Tick relevant boxes, this PR is-a or has-a:

• [ ] Bugfix
  • [ ] Regression tests
  • [ ] ChangeLog updates (for next release)
• [ ] Feature
  • [ ] YANG model change => revision updated?
  • [ ] Regression tests added?
  • [ ] ChangeLog updates (for next release)
  • [ ] Documentation added?
• [ ] Test changes
  • [ ] Checked in changed Readme.adoc (make test-spec)
  • [ ] Added new test to group Readme.adoc and yaml file
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (please detail in commit messages)
• [ ] Build related changes
• [ ] Documentation content changes
  • [ ] ChangeLog updated (for major changes)
• [ ] Other (please describe):

[troglobit]

Should include a fixes line to close https://github.com/kernelkit/infix/issues/773

Other than that it looks good to me. But I'll leave the full review to @mattiaswal 👍