[action] [PR:16494] [dhcp_relay] Add test case to verify dhcp6relay LLA waiting logic

[mssonicbld]

Description of PR

Summary:
Fixes #16344

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
• Skipped for non-supported platforms
• Add ownership here(Microsft required only)
• Test case improvement

Back port request

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

Approach

What is the motivation for this PR?

We add wait LLA logic in dhcp6relay with sonic-net/sonic-dhcp-relay#52
Current PR is to add test for it to verify dhcp6relay would work well when LLA is missing

How did you do it?

Modify test_interface_binding:

1. Remove LLA for Vlans
2. Restart dhcp_relay container
3. Verify whether sockets for LLA are not established
4. Add LLA back
5. Verify whether sockets for LLA are established

How did you verify/test it?

Run test_dhcpv6_relay.py

collected 6 items 

dhcp_relay/test_dhcpv6_relay.py::test_interface_binding PASSED [ 16%]
dhcp_relay/test_dhcpv6_relay.py::test_dhcpv6_relay_counter PASSED [ 33%]
dhcp_relay/test_dhcpv6_relay.py::test_dhcp_relay_default PASSED [ 50%]
dhcp_relay/test_dhcpv6_relay.py::test_dhcp_relay_after_link_flap PASSED [ 66%]
dhcp_relay/test_dhcpv6_relay.py::test_dhcp_relay_start_with_uplinks_down PASSED [ 83%]
dhcp_relay/test_dhcpv6_relay.py::TestDhcpv6RelayWithMultipleVlan::test_dhcp_relay_default[3] PASSED [100%]

================================================================================================================================= warnings summary =================================================================================================================================
../../../../usr/local/lib/python3.8/dist-packages/paramiko/transport.py:236
 /usr/local/lib/python3.8/dist-packages/paramiko/transport.py:236: CryptographyDeprecationWarning: Blowfish has been deprecated
 "class": algorithms.Blowfish,

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
--------------------------------------------------------------------------------------------- generated xml file: /var/src/sonic-mgmt-int/tests/logs/dhcp_relay/test_dhcpv6_relay.xml ----------------------------------------------------------------------------------------------
===================================================================================================================== 6 passed, 1 warning in 967.94s (0:16:07) =====================================================================================================================

Any platform specific information?

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

Documentation

[mssonicbld]

/azp run

[mssonicbld]

Original PR: #16494

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Azure Pipelines successfully started running 1 pipeline(s).

[mssonicbld]

/azp run Azure.sonic-mgmt

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).