Fix Unexpected DHCP iptables rules for test_cacl_application_dualtor …

…case (#11878)

Description of PR
Summary:
Fixes # (issue)
On latest master image, test_cacl_application_dualtor case could fail due to the following reason:
Failed: Missing expected iptables rules: {'-A DHCP -m mark --mark 0x67005 -j DROP'}

This is caused by the oscillation logic: sonic-net/sonic-linkmgrd#221

As there is no icmp_responder running, the mux will start flap, if it flaps betrween expected_dhcp_rules_for_standby fixture and
the real iptables check, there could be some unexpected dhcp iptables which will cause case failure.

What is the motivation for this PR?
Fix Unexpected DHCP iptables rules for test_cacl_application_dualtor

How did you do it?
test_cacl_application_dualtor is used to verify dhcp iptables on dualtor, not oscillation.
Before dualtor case, set mux mode to manual
sudo config mux mode manual all
in test teardown, run to set to auto back.
sudo config mux mode auto all

How did you verify/test it?
Run cacl/test_cacl_application.py::test_cacl_application_dualtor on dualtor testbed against master image.

Any platform specific information?

tests/cacl/test_cacl_application.py

@@ -28,7 +28,9 @@ def duthost_dualtor(request, upper_tor_host, lower_tor_host):       # noqa F811
     else:
         logger.info("Select upper tor...")
         dut = upper_tor_host
-    return dut
+    dut.shell("sudo config mux mode manual all")
+    yield dut
+    dut.shell("sudo config mux mode auto all")
 
 
 @pytest.fixture