Link Flap: Adding interface and drop counter checks for continuous link flap test.

[rraghav-cisco]

Description of PR

Summary:
Adding checks for both interface counters and drop counters in continuous link flap test. This is to catch any problem that will cause the counters to go up drastically when the interfaces are flapping, or going down.

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505
• 202511

Approach

What is the motivation for this PR?

We saw some issues in interfaces where the ports were flapping, and the drop counters were going up drastically. This PR attempts to modify the existing test case to catch this condition.

How did you do it?

Added drop and interface counter checks to the test_cont_link_flap test.

How did you verify/test it?

Ran it on our platform:

sonic@sonic-ucs-m6-33:~/test_logs/ixia/link-flap$ cd 2026-02-09-18-59-11
sonic@sonic-ucs-m6-33:~/test_logs/ixia/link-flap/2026-02-09-18-59-11$ less tr_2026-02-09-18-59-11.xml 
<?xml version="1.0" encoding="utf-8"?><testsuites><testsuite name="pytest" errors="0" failures="0" skipped="0" tests="1" time="3511.970" timestamp="2026-02-09T18:59:12.670561" hostname="sonic-ucs-m6-33"><properties><property name="topology" value="t0" /><property name="testbed" value="super-t0" /><property name="timestamp" value="2026-02-09 18:59:50.740308" /><property name="host" value="laguna-t0-1-dut" /><property name="asic" value="cisco-8000" /><property name="platform" value="x86_64-8122_64ehf_o-r0" /><property name="hwsku" value="Cisco-8122-O128S2" /><property name="os_version" value="azure_cisco_202511.34666-dirty-20260114.171002" /></properties><testcase classname="platform_tests.link_flap.test_cont_link_flap.TestContLinkFlap" name="test_cont_link_flap[laguna-t0-1-dut]" file="platform_tests/link_flap/test_cont_link_flap.py" line="128" time="3488.791"><properties><property name="start" value="2026-02-09 18:59:35.844803" /><property name="end" value="2026-02-09 19:57:44.637165" /></properties></testcase></testsuite></testsuites>
sonic@sonic-ucs-m6-33:~/test_logs/ixia/link-flap/2026-02-09-18-59-11$ 

[mssonicbld]

/azp run

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[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[rraghav-cisco]

@yxieca : Regarding your comments in the older version of the PR(#22581):

1. I have verified that the show_and_parse actually returns the same order of interfaces. If the order of interfaces is different before and after the tests, that is an error/bug in DUT. It should be caught.
2. Missing fields is also similar to (1), its a problem in DUT, should be fixed. But if a particular platform won't support some of the fields, the code may have to be conditionally modified for that platform.