BFD stays for neighbor after overwriting with a config that doesn't have it

[oribon]

Description

Spotted on frr-k8s ci. When applying a config that has BFD and then one that does not via the frr-reload.py script the neighbor still has bfd configured, e.g:

neighbor 10.x.x.x bfd

Version

bug happens on both 9.1.0, 9.1.3.
on 10.2.1 it works as expected

How to reproduce

first.conf.txt
second.conf.txt
(the ips are not sensitive - what we use in ci that deploys a kind cluster)
Always reproducible by appling first then second:

python3 /usr/lib/frr/frr-reload.py --reload --overwrite --stdout first.conf
python3 /usr/lib/frr/frr-reload.py --reload --overwrite --stdout second.conf

Expected behavior

the neighbor to have no BFD after applying a config that has no bfd.

Actual behavior

the neighbor still has bfd configured:

neighbor 10.x.x.x bfd

Additional context

I think this can be solved by bringing #15536 to 9.x
Thanks!

Checklist

• I have searched the open issues for this bug.
• I have not included sensitive information in this report.

[Jafaral]

Why not upgrade to a newer version?