mpls-conf: T915: Add LDP import and export control

[Cheeze-It]

In this commit we added the ability to control import and export
of LDP FECs. This allows for an operator to specify which to
filter on ingress, and which to not announce on egress.

Change Summary

In this change we are adding more functionality to LDP. We are specifically adding the ability to control the import and export of the routes that LDP deals with. this shouldn't break any existing functionality.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

https://phabricator.vyos.net/T915

Component(s) name

LDP

Proposed changes

We added the tie into FRR for access lists to be referenced and then added for import and export control. This functionality was added for both IPv4 and IPv6. Although the access list approach is a little bit cumbersome it does work as one expects.

How to test

I tested the changes in a GNS3 lab with Junipers and VyOS routers. The VyOS routers did correctly import and export the routes properly once the access list was properly configured. That all being said, configuring access lists for imports seems to work as one expects but seems unwieldy. It does work as expected though.

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly