[chassis][fabric][packet-chassis] Add tests to test fabric ports on packet chassis

[smaheshm]

Description

On packet chassis line cards are connected to each other with L2 LAG ports. Example test cases:

• L2 interface port counters, drop counters
• Port queue counters?
• LAG Link connectivity/reachability
• LAG member port flap, port down
• LAG ECMP

Describe the results you received:

Describe the results you expected:

Additional information you deem important:

**Output of `show version`:**

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**Attach debug file `sudo generate_dump`:**

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[rlhui]

@bmridul , this needs more triaging and requirements definition, please also work with @abdosi /cisco internal team to define the test cases. Thanks.

[rlhui]

@abdosi we may close this and open more specific tests if any?

[arlakshm]

@anamehra to check and update

[arlakshm]

@anamehra to check what is the current coverage and what is missing in the current tests.

[arlakshm]

@anamehra to update the issue on the plan to fix the missing test coverage for the backend ports.

[vperumal]

Hi https://github.com/sonic-net/sonic-mgmt/blob/master/tests/bfd/test_bfd_static_route.py - This script covers most of the fabric side tests. We will add support for counters to get more coverage.