docs: BGPv2 CP documentation update

[dswaffordcw]

Please ensure your pull request adheres to the following guidelines:

• For first time contributors, read Submitting a pull request
• All code is covered by unit and/or runtime tests where feasible.
• All commits contain a well written commit description including a title,
  description and a Fixes: #XXX line if the commit addresses a particular
  GitHub issue.
• If your commit description contains a Fixes: <commit-id> tag, then
  please add the commit author[s] as reviewer[s] to this issue.
• All commits are signed off. See the section Developer’s Certificate of Origin
• Provide a title or release-note blurb suitable for the release notes.
• Are you a user of Cilium? Please add yourself to the Users doc
• Thanks for contributing!

This PR updates Cilium's documentation for the BGPv2 Control Plane. In specific, it adds a caution note for the transport section.

This update was prompted by https://cilium.slack.com/archives/C53TG4J4R/p1718753533112889. In that, I had started a thread regarding extremely slow convergence after a neighbor reset event. In my testing, I observed a 2+ minute delay before Cilium's BGP session re-established with a remote BGP speaker after issuing a hard reset of the session from the remote speaker's side.

After removing:

spec:
  transport:
    localPort: 179
    peerPort: 179

From my CiliumBGPPeerConfig, what previously took 2+ minutes was now less than 10 seconds.

Documentation update for BGPv2 transport configuration

Testing

For testing, I ran make html from the Documentation directory. Then I opened the modified HTML file from _build/. A screenshot is shown below.

[maintainer-s-little-helper]

Commit 9dd9f2f does not match "(?m)^Signed-off-by:".

Please follow instructions provided in https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#developer-s-certificate-of-origin

[maintainer-s-little-helper]

Commit 9dd9f2f does not match "(?m)^Signed-off-by:".

Please follow instructions provided in https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#developer-s-certificate-of-origin

[lambdanis]

/test

[harsimran-pabla]

One minor comment, thanks for adding this in docs. 🙏

[dswaffordcw]

@harsimran-pabla @rastislavs How's this look now?

I removed all references to localPort, but kept the transport section and moved it later. It now describes configuring only the remote peer's port.

In the main example, I removed the transport section entirely and removed connectRetryTimerSeconds.

[harsimran-pabla]

I removed all references to localPort, but kept the transport section and moved it later. It now describes configuring only the remote peer's port.

That's great. After discussing this with @YutaroHayakawa, we decided to remove the LocalPort setting. But since CRD has already been published, we will mark the field as deprecated for now and remove it after two releases.

[harsimran-pabla]

/test