[Test Gap][PFCWD][T0&T1][Mellanox] PFC watchdog test on testbed with Non-Mellanox leaf-fanout

[bingwang-ms]

Test Gap Description

The PFC watchdog test set is flaky on Non-Mellanox leaf-fanout. Flaky test cases include

• pfcwd/test_pfcwd_function.py
• pfcwd/test_pfcwd_warm_reboot.py
• pfcwd/test_pfcwd_timer_accuracy.py

It's because PR sonic-net/sonic-swss#3036 updated the PFC storm detection logic, which made PFC watchdog can hardly be triggered by sending PFC pause frames with pfc_gen.py on leaf-fanout.
The gap doesn't exist on testbed with Mellanox leaf fanout as there is a dedicated script which leverages ASIC to send PFC pause frames. https://github.com/sonic-net/sonic-mgmt/blob/master/ansible/roles/test/files/mlnx/docker-tests-pfcgen-asic/pfc_gen.py

Test Plan

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Test environment

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Attach files (if any)

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[bingwang-ms]

@developfast @kperumalbfn FYI

[developfast]

@bingwang-ms are you sure about this? I was able to trigger pfcwd with the script on all broadcom platforms when reproducing a prod issue.