Orchagent receives neighbor DEL operation when the reference count of the neighbor is not zero after reboot

[shi-su]

Description
The orchagent receives neighbor DEL operation when the reference count of the neighbor is not zero with ping traffic after reboot (cold/fast/warm).

Steps to reproduce the issue
Run warm/fast-reboot test (advanced-reboot). Confirmed the issue also happens with cold reboot with the same ping traffic of warm/fast-reboot test.

Describe the results you received
Orchagent receives neighbor DEL operation. The operation fails due to a non-zero reference count.

Oct 26 22:23:15.259716 vlab-01 INFO swss#orchagent: :- removeNeighbor: Failed to remove still referenced neighbor 1e:92:d0:9e:6d:64 on PortChannel0002
Oct 26 22:23:15.259851 vlab-01 INFO swss#orchagent: :- removeNeighbor: Failed to remove still referenced neighbor 26:74:37:ff:3b:fa on PortChannel0004

Describe the results you received
Expect not to receive neighbor deletion operations with reference counter.

[shi-su]

@qiluo-msft @lguohan @zhenggen-xu for visibility

[prsunny]

Looks like related to this - sonic-net/sonic-buildimage#4400 (comment)

[shi-su]

Looks like related to this - Azure/sonic-buildimage#4400 (comment)

Yes, I just submitted #1485 to resolve it for neighorch and fix sonic-net/sonic-buildimage#4400. While the source of the DEL operation remains unknown, this issue aims to track the source of the unexpected operation