What is the motivation for this PR?
The new test is a poorly written IPV6 variant of testQosSaiDscpQueueMapping. It is expected to fail across all platforms/topolgies because qos/test_qos_sai.py cannot support IPV6 variant of any of it's testcase because IPV6 is disabled on the DUT by qos_sai_base.py: https://github.com/sonic-net/sonic-mgmt/blob/master/tests/qos/qos_sai_base.py#L1811-L1826 Also the changes made for this test touch class scoped fixtures which causes all the other testcases to error out as well.

How did you do it?
Revert #10941 as well as the following fixes that were made to get around the issue

Fix qos/test_qos_sai.py #12334
Skip IPV6 variant of testQosSaiDscpQueueMapping if IPV6 is not config… #12834

How did you verify/test it?
Verfied on T0, T1 and T0-dualTor, #126 was not seen.

…ured. (sonic-net#12834)

What is the motivation for this PR?
IPV6 variant of the test fails

qos/test_qos_sai.py::TestQosSai::testQosSaiDscpQueueMapping[single_asic-ipv6]
---------------------------------------------------------------------------------------- live log call ----------------------------------------------------------------------------------------
06:25:52 __init__.pytest_runtest_call             L0040 ERROR  | Traceback (most recent call last):
  File "/usr/local/lib/python3.8/dist-packages/_pytest/python.py", line 1788, in runtest
    self.ihook.pytest_pyfunc_call(pyfuncitem=self)
  File "/usr/local/lib/python3.8/dist-packages/pluggy/_hooks.py", line 493, in __call__
    return self._hookexec(self.name, self._hookimpls, kwargs, firstresult)
  File "/usr/local/lib/python3.8/dist-packages/pluggy/_manager.py", line 115, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
  File "/usr/local/lib/python3.8/dist-packages/pluggy/_callers.py", line 113, in _multicall
    raise exception.with_traceback(exception.__traceback__)
  File "/usr/local/lib/python3.8/dist-packages/pluggy/_callers.py", line 77, in _multicall
    res = hook_impl.function(*args)
  File "/usr/local/lib/python3.8/dist-packages/_pytest/python.py", line 194, in pytest_pyfunc_call
    result = testfunction(**testargs)
  File "/data/tests/qos/test_qos_sai.py", line 1337, in testQosSaiDscpQueueMapping
    "src_port_ip": dutConfig["testPorts"]["src_port_ipv6"],
KeyError: 'src_port_ipv6'

FAILED
This is because IPV6 is disabled on the DUT for the entire qos/test_qos_sai.py: https://github.com/sonic-net/sonic-mgmt/blob/master/tests/qos/qos_sai_base.py#L1818

How did you do it?
The IPV6 variant of this test needs more work or probably should be a new test module altogether therefore skipping the test for now if IPV6 is not found for the interfaces.

How did you verify/test it?
Ran the test with with 202311 image

qos/test_qos_sai.py::TestQosSai::testQosSaiDscpQueueMapping[single_asic-ipv6] SKIPPED (Skip IPV6 variant as IPV6 not configured)                                                        [100%]
Any platform specific information?