Fix qos/test_qos_sai.py teardown. (sonic-net#11934)

Regression introduced by sonic-net#10651 for dualtor.

The config_reload in the fixture `dut_disable_ipv6` waits until all critical processes are up after issuing config reload command and it timeouts in case of dualtor because mux container doesn't come up. Mux container is disabled by another fixture in the same file `stopServices`. These two fixtures have no dependency on each other hence the execution can happen in any order, so if the teardown of `dut_disable_ipv6` happens before `stopServices` then this issue is seen.

Author: vivekverma-arista

tests/qos/qos_sai_base.py

@@ -1113,7 +1113,7 @@ def updateIptables(self, duthosts, get_src_dst_asic_and_duts, swapSyncd_on_selec
 
     @pytest.fixture(scope='class')
     def stopServices(
-        self, duthosts, get_src_dst_asic_and_duts,
+        self, duthosts, get_src_dst_asic_and_duts, dut_disable_ipv6,
         swapSyncd_on_selected_duts, enable_container_autorestart, disable_container_autorestart, get_mux_status, # noqa F811
         tbinfo, upper_tor_host, lower_tor_host, toggle_all_simulator_ports):  # noqa F811
         """