zebra: avoid having speed set to UINT32_MAX (backport #10151)

[mergify]

This is an automatic backport of pull request #10151 done by Mergify.
Cherry-pick of e3c62b2 has failed:

On branch mergify/bp/stable/9.1/pr-10151
Your branch is ahead of 'origin/stable/9.1' by 1 commit.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit e3c62b2ae.
  (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)

Changes to be committed:
	modified:   doc/user/zebra.rst
	modified:   yang/frr-zebra.yang

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   zebra/zebra_cli.c

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

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