frr: T6600: apply pending upstream patch for ospfd ldp-sync

[c-po]

Change Summary

When enabling mpls ldp-sync under router ospf ospfd configures SET_FLAG(ldp_sync_info->flags, LDP_SYNC_FLAG_IF_CONFIG) so internally knowing that the ldp-sync feature is enabled.

However the flag is not cleared when turning of the feature using no mpls ldp-sync!

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://vyos.dev/T6600

Related PR(s)

• smoketest: T6600: ospf: enable MPLS LDP on dummy interfaces vyos-1x#3838

Component(s) name

FRR

Proposed changes

How to test

Smoketests

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

[github-actions]

👍
No issues in PR Title / Commit Title