cli: hide internal interfaces in tabcomplete

[rical]

Description

Don't show "internal" interfaces in "show interface name" tab completion.

Side note

I initially implemented this in the show command, as "show ifnames". It worked but was unreasonably slow for some reason, perhaps due to the show init code that does resize and such. As there's no variables involved I abandoned that approach and inlined it instead.

Checklist

• [x] Bugfix
  • [ ] Regression tests
  • [ ] ChangeLog updates (for next release)
• [ ] Feature
  • [ ] YANG model change => revision updated?
  • [ ] Regression tests added?
  • [ ] ChangeLog updates (for next release)
  • [ ] Documentation added?
• [ ] Code style update (formatting, renaming)
• [ ] Refactoring (please detail in commit messages)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Other (please describe):