bgpd: fix unconfigure asdot neighbor (backport #17582)

[mergify]

The below command is not successfull on an existing as dot peer

no neighbor 10.0.0.2 remote-as 1.1
% Create the peer-group or interface first

Handle the case where the remote-as argument can be an ASNUM.

Fixes: 8079a41 ("lib, bgp: add initial support for asdot format")

---

This is an automatic backport of pull request #17582 done by Mergify.

[mergify]

Cherry-pick of 12a9ca4 has failed:

On branch mergify/bp/stable/9.1/pr-17582
Your branch is up to date with 'origin/stable/9.1'.

You are currently cherry-picking commit 12a9ca4de6.
  (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_vty.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]

Replaced by #17597.