Test BGP 4 byte as trans - T2 Update

[sresri2]

Description of PR

Summary:
Enable test_bgp_4-byte_as_trans on T2 multi-ASIC by fixing namespace-scoped vtysh on neighbor devices.

DUT vtysh commands already used per-ASIC logic, but two neighbor-side issues broke multi-ASIC runs. neigh_cli_options used the neighbor hostname string instead of the neighbor host object, and the final received-routes check on neigh2 used global vtysh with no namespace.

Changes:

• Fix neigh_cli_options to use ASIC index to get namespace.
• Added and used separate cli options for neigh2 and for final received-routes command.
• Remove the T2 conditional skip for this test.

Type of change

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

Back port request

• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605

Tracking issue/work item for backport/cherry-pick request (GitHub issue or Microsoft ADO):
Failure type:

Tested branch

• master
• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605
• N/A

Test result

N/A

Approach

What is the motivation for this PR?

On multi-ASIC T2, neighbor vtysh commands should target the correct ASIC namespace. The setup had a bug resolving neigh1’s namespace, and the final route verification on neigh2 fully omitted namespace scoping.

How did you do it?

• Fixed neigh_cli_options to call get namespace on host object rather than host string.
• Updated the final received routes command on neigh2 to use the added neigh2_cli_options.
• Removed the T2 skip for this test.

How did you verify/test it?

• Code review for quality and functionality.
• Code review for consistency with other similar T2 updates / tests.
• GitHub PR checks / pipeline for full validation.

Any platform specific information?

N/A

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

Existing test, logic updated for T2.

Documentation

N/A.

[mssonicbld]

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[github-actions]

@StormLiangMS @wangxin @yxieca A user wants to merge changes to the conditional mark files into master. Please review.