change swapsyncd to module level. (#15501)

Description of PR
Summary:
change swapsyncd and disable_ipv6 to module level.
Running time on T2 reduced by around 140 minutes (from 685.08 minutes to 543.95 minutes).

Existing code will do swapSyncd for selected dut only in each iteration. In a T2 full test, it was around 8 LC which needs to do swapsyncd, including setup and teardown for each iteration.

select_src_dst_dut_and_asic	selected DUT to do swapsyncd (Existing)
single_asic	one downstream LC
single_dut_multi_asic	one downstream LC
multi_dut_longlink_to_shortlink	one upstream LC, one downstream LC
multi_dut_shortlink_to_shortlink	two downstream LC
multi_dut_shortlink_to_longlink	one upstream LC, one downstream LC
After the fix, swapsyncd will be done for all LCs at the beginning of the test. Saved around 5 LC swapsyncd time

select_src_dst_dut_and_asic	selected DUT to do swapsyncd (after fix)
Setup	one upstream LC, two downstream LC
single_asic	none
single_dut_multi_asic	none
multi_dut_longlink_to_shortlink	none
multi_dut_shortlink_to_shortlink	none
multi_dut_shortlink_to_longlink	none
Teardown	one upstream LC, two downstream LC
Type of change
 Bug fix
 Testbed and Framework(new/improvement)
 Test case(new/improvement)
Back port request
 202012
 202205
 202305
 202311
 202405
Approach
What is the motivation for this PR?
Reduce the run time for test_qos_sai module.

How did you do it?
change the swapsyncd fixture to module level. replace all dut with rpcsyncd container, instead of replacing selected dut multiple times for each iteration.

How did you verify/test it?
verified the physical testbed.

co-authorized by: jianquanye@microsoft.com

tests/qos/qos_sai_base.py

@@ -563,8 +563,8 @@ def __assignTestPortIps(self, mgFacts, topo):
 
         return dutPortIps
 
-    @pytest.fixture(scope='class')
-    def swapSyncd_on_selected_duts(self, request, duthosts, get_src_dst_asic_and_duts, creds, tbinfo, lower_tor_host): # noqa F811
+    @pytest.fixture(scope='module')
+    def swapSyncd_on_selected_duts(self, request, duthosts, creds, tbinfo, lower_tor_host): # noqa F811
         """
             Swap syncd on DUT host
 
@@ -575,6 +575,10 @@ def swapSyncd_on_selected_duts(self, request, duthosts, get_src_dst_asic_and_dut
             Returns:
                 None
         """
+        if 'dualtor' in tbinfo['topo']['name']:
+            dut_list = [lower_tor_host]
+        else:
+            dut_list = duthosts.frontend_nodes
         swapSyncd = request.config.getoption("--qos_swap_syncd")
         public_docker_reg = request.config.getoption("--public_docker_registry")
         try:
@@ -586,12 +590,12 @@ def swapSyncd_on_selected_duts(self, request, duthosts, get_src_dst_asic_and_dut
                     new_creds['docker_registry_password'] = ''
                 else:
                     new_creds = creds
-                for duthost in get_src_dst_asic_and_duts["all_duts"]:
+                for duthost in dut_list:
                     docker.swap_syncd(duthost, new_creds)
             yield
         finally:
             if swapSyncd:
-                for duthost in get_src_dst_asic_and_duts["all_duts"]:
+                for duthost in dut_list:
                     docker.restore_default_syncd(duthost, new_creds)
 
     @pytest.fixture(scope='class', name="select_src_dst_dut_and_asic",
@@ -1872,11 +1876,15 @@ def populateArpEntries(
         yield
         return
 
-    @pytest.fixture(scope='class', autouse=True)
-    def dut_disable_ipv6(self, duthosts, get_src_dst_asic_and_duts, tbinfo, lower_tor_host, # noqa F811
-                         swapSyncd_on_selected_duts):
+    @pytest.fixture(scope='module', autouse=True)
+    def dut_disable_ipv6(self, duthosts, tbinfo, lower_tor_host, swapSyncd_on_selected_duts): # noqa F811
+        if 'dualtor' in tbinfo['topo']['name']:
+            dut_list = [lower_tor_host]
+        else:
+            dut_list = duthosts.frontend_nodes
+
         all_docker0_ipv6_addrs = {}
-        for duthost in get_src_dst_asic_and_duts['all_duts']:
+        for duthost in dut_list:
             try:
                 all_docker0_ipv6_addrs[duthost.hostname] = \
                     duthost.shell("sudo ip -6  addr show dev docker0 | grep global" + " | awk '{print $2}'")[
@@ -1891,14 +1899,14 @@ def dut_disable_ipv6(self, duthosts, get_src_dst_asic_and_duts, tbinfo, lower_to
 
         yield
 
-        for duthost in get_src_dst_asic_and_duts['all_duts']:
+        for duthost in dut_list:
             duthost.shell("sysctl -w net.ipv6.conf.all.disable_ipv6=0")
             if all_docker0_ipv6_addrs[duthost.hostname] is not None:
                 logger.info("Adding docker0's IPv6 address since it was removed when disabing IPv6")
                 duthost.shell("ip -6 addr add {} dev docker0".format(all_docker0_ipv6_addrs[duthost.hostname]))
 
         # TODO: parallelize this step.. Do we really need this ?
-        for duthost in get_src_dst_asic_and_duts['all_duts']:
+        for duthost in dut_list:
             config_reload(duthost, config_source='config_db', safe_reload=True, check_intf_up_ports=True)
 
     @pytest.fixture(scope='class', autouse=True)