[action] [PR:17511] Fixed two issues causing test failures in test_vxlan_bfd_tsa.py

[mssonicbld]

Description of PR

This PR fixes test failures in test_vxlan_bfd_tsa.py::Test_VxLAN_BFD_TSA. These failures were observed on some platforms such as Mellanox msn4600c and Cisco 8102.

Summary:
Fixes #15728
Microsoft ADO ID: 31220198
The following two fixed were applied for test_tsa_case4, test_tsa_case5, and test_tsa_case6:

1. Replaced the manual execution of sudo config reload -y with a call to config_reload so that all interfaces and ports are up before configuring a VXLAN on the switch.
2. Added a check after configuring VNET routes to ensure that VNET routes are applied to the ASIC DB before running PTF tests.

Type of change

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

Back port request

• 202012
• 202205
• 202305
• 202311
• 202405
• 202411

Approach

What is the motivation for this PR?

test_tsa_case4, test_tsa_case5, and test_tsa_case6 failed on some platforms such as Mellanox msn4600c and Cisco 8102.

How did you do it?

By using config_reload instead of executing sudo config reload -y directly and making sure that VNET routes are applied to the ASIC DB before running PTF tests.

How did you verify/test it?

Ran the tests on a Mellanox msn4600c switch.
Note: In order for the tests to pass, the image running on the switch must have the following fix from sonic-utilities:
revert YANG check in db_migrator

Any platform specific information?

N/A

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

N/A

[mssonicbld]

/azp run

[mssonicbld]

Original PR: #17511

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