Enable dip_sip and mtu test on DT2 topology

[bingwang-ms]

Description of PR

Summary:
This PR is to enable two tests on LT2 and FT2.

• tests/ipfwd/test_dip_sip.py
• tests/ipfwd/test_mtu.py

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

Approach

What is the motivation for this PR?

This PR is to enable two tests on LT2 and FT2.

How did you do it?

1. Update tests/common/plugins/conditional_mark/tests_mark_conditions.yaml to add LT2 and FT2 into supported topologies
2. Update test code to add LT2 and FT2 to topology marker

How did you verify/test it?

The change is verified on a physical testbed.

collected 1 item                                                                                                                                                                                                              

ipfwd/test_dip_sip.py::test_dip_sip[None] PASSED                                                                                                                                                      [100%]

collected 2 items                                                                                                                                                                                                             

ipfwd/test_mtu.py::test_mtu[1514] PASSED                                                                                                                                                         [ 50%]
ipfwd/test_mtu.py::test_mtu[9114]  ^HPASSED                                                                                                                                                         [100%]

Any platform specific information?

No.

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

Not a new test.

Documentation

[mssonicbld]

/azp run

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