Fix test_check_show_lpmode case

[weiguo-nvidia]

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Description of PR

Summary: Fix test_check_show_lpmode case Fixes # (issue)

1. Currently the test_check_show_lpmode case use xcvr_skip_list function to check lpmode for only supported interface, but the code passes all the output of show interface transceiver lpmode to validate_transceiver_lpmode function, then the function checks each interface lpmode. This is incorrect. Fix it.

For example, if the interface lpmode is like this "['Ethernet0 N/A', 'Ethernet1 Off']", Ethernet0 is RJ45 and no lpmode check is needed. Ethernet1 needs to check lpmode

• In the current logic, Ethernet0 does not check lpmode, which is correct.
• Ethernet1 needs to check lpmode, but the code passes all the output (['Ethernet0 N/A', 'Ethernet1 Off']) of the command to the function validate_transceiver_lpmode. It checks each item and finds that Ethernet0 lpmode is "N/A", then the case fails. This is incorrect

2. Move the "check if header exists" test from validate_transceiver_lpmode to test_check_show_lpmode. So the header only check one time.

Type of change

• [x] Bug fix
• [ ] Testbed and Framework(new/improvement)
• [ ] Test case(new/improvement)

Back port request

• [ ] 202012
• [ ] 202205
• [ ] 202305
• [ ] 202311
• [x] 202405

Approach

What is the motivation for this PR?

How did you do it?

How did you verify/test it?

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[bingwang-ms]

@prgeor Can you help review?

[prgeor]

@mihirpat1 can review?

[weiguo-nvidia]

Hi @bingwang-ms ,

@mihirpat1 had approved the change, could you help merge it, thanks!

[bingwang-ms]

/azp run Azure.sonic-mgmt

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[bingwang-ms]

PR checker got stuck. Just re-triggered it

[mssonicbld]

@weiguo-nvidia PR conflicts with 202405 branch

[weiguo-nvidia]

conflicts with 202405 branch

Hi @mssonicbld ,

I create PR #15417 to submit the same fix in 202405 branch, could you help review it?