[ssw][ha][202511] cherry-pick `custom_bfd` changes#4114

Merged

vmittal-msft merged 2 commits intosonic-net:202511from

Jan 9, 2026

Commits on Jan 9, 2026

[vnetorch] missing handling of rx and tx interval of monitoring session (#3878)
zjswhhh
committed
[ssw][ha] introducing `custom_bfd` and BfdMonitorOrch to support primary/secondary NHG switchover (#3922)
zjswhhh
committed