Fix qos node selection for single-asic in qos_sai_base test

[veronica-arista]

Description of PR

Summary: The search for shortlink linecard logic added in PR https://github.com/sonic-net/sonic-mgmt/pull/14925 does not verify that a DUT is multi-asic for the single_dut_multi_asic tests and incorrectly tries to access two asics on a single-asic DUT.

Add a check for multi-asic DUT in the shortlink linecard selection logic.

Fixes #15073

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?

Run the test on out t2min chassis both with single-asic and multi-asic DUTs

Any platform specific information?

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

Documentation