troubleshooting: T8608: document TCP ping (backport #1878)

[mergify]

Change summary

Document the new TCP ping operational command added for T8608.

The documented syntax is:

ping tcp <host> port <port> [count <n>] [interface <ifname>] [vrf <name>] [source-address <address>]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe): documentation

Related Task(s)

• https://vyos.dev/T8608

Related PR(s)

• Code PR: ping: T8608: add TCP connect probe vyos-1x#5164

How to test / Smoketest result

$ git diff --check -- docs/troubleshooting/connectivity.rst
OK

Sphinx dummy builder completed successfully for the changed page with no warnings from docs/troubleshooting/connectivity.rst.

Full Sphinx HTML build was attempted and hit existing unrelated documentation errors outside this change.

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

---

This is an automatic backport of pull request #1878 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 7ae07ad has failed:

On branch mergify/bp/sagitta/pr-1878
Your branch is up to date with 'origin/sagitta'.

You are currently cherry-picking commit 7ae07ade.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   docs/troubleshooting/connectivity.md

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[andamasov]

Closing — backport to sagitta is incorrect for two reasons:

1. Feature doesn't exist in 1.4. vyos-1x/op-mode-definitions/ping.xml.in@sagitta only defines ICMP ping; no tcp subcommand. The TCP ping feature was added under T8608 for rolling/1.5+. Backporting the documentation would create inaccurate docs on the 1.4 branch (documenting a command that doesn't run).

2. Structural mismatch (only relevant if (1) didn't apply). sagitta has no docs/troubleshooting/connectivity.md — all troubleshooting content lives in docs/troubleshooting/index.md in RST-inside-MyST style. The cherry-pick conflict that opened this PR (deleted by us: docs/troubleshooting/connectivity.md) reflects that.

If/when sagitta gets the TCP ping feature, a manual port to index.md (with RST-style .. opcmd:: inside an eval-rst block) would be the right approach. For now, this backport should not land.