fix: support IPv6 BGP peerings

[apalrd]

Description

Updates BGP dialog / API to support v4 and v6 peers. Note that the address family of the BGP session has no relation to the data sent over BGP, the BGP session still only supports ipv4 afi.

The regex should properly support v4, v6, v6 link-local with scope (fe80::1%eth0), v6-mapped-v4 (::ffff:192.168.1.1), and v6-translated-v4 (6f:ff9b::192.168.1.1).

I tested this with a v6 peer (BIRD3) and the session came up and exchanged routes without issues. I have not updated test cases, I'm not a regular Go dev so I'm not familiar enough with them.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[ghislainbourgeois]

Thank you very much for this PR!

Regarding the test, if you can look into internal/api/server/api_bgp_test.go, there is a block at line 1010 that checks that v6 is rejected, can you remove that block so that the tests pass?

Don't worry about adding new tests, I am working on IPv6 features also, and I can add the missing tests later.

[apalrd]

Updated both

Comment was addressed