bgpd: Unset advertised capabilities if capability is disabled (backport #15514)

[mergify]

This is an automatic backport of pull request #15514 done by Mergify.
Cherry-pick of 77102e8 has failed:

On branch mergify/bp/dev/10.0/pr-15514
Your branch is up to date with 'origin/dev/10.0'.

You are currently cherry-picking commit 77102e853.
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  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
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	both modified:   bgpd/bgp_packet.c

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

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[mergify]

Cherry-pick of 77102e8 has failed:

On branch mergify/bp/dev/10.0/pr-15514
Your branch is up to date with 'origin/dev/10.0'.

You are currently cherry-picking commit 77102e853.
  (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 <file>..." to mark resolution)
	both modified:   bgpd/bgp_packet.c

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

[ton31337]

Created manual backport #15521, closing this.