[tests] add support for enable/disable OT mdns (#11660)

tests/scripts/thread-cert/border_router/test_dnssd_server_multi_border_routers.py

@@ -137,9 +137,9 @@ class TestDnssdServerOnMultiBr(thread_cert.TestCase):
         self.simulator.go(5)
 
         # start BR2 late to ensure it doesn't have mDNS cache
-        br2.start_mdns_service()
         br2.start_otbr_service()
         br2.start()
+        br2.start_mdns_service()
 
         self.simulator.go(config.BORDER_ROUTER_STARTUP_DELAY)
         br2.dns_upstream_query_state = False

tests/scripts/thread-cert/node.py

@@ -177,9 +177,23 @@ class OtbrDocker:
         self.bash('service otbr-agent stop')
 
     def stop_mdns_service(self):
+        self.send_command('mdns disable')
+        # The OT build may not include mdns, so ignore `InvalidCommand` errors.
+        try:
+            self._expect_result(r'Done')
+        except Exception as ex:
+            if 'InvalidCommand' not in str(ex):
+                raise
         self.bash('service avahi-daemon stop; service mdns stop; !(cat /proc/net/udp | grep -i :14E9)')
 
     def start_mdns_service(self):
+        self.send_command('mdns enable')
+        # The OT build may not include mdns, so ignore `InvalidCommand` errors.
+        try:
+            self._expect_result(r'Done')
+        except Exception as ex:
+            if 'InvalidCommand' not in str(ex):
+                raise
         self.bash('service avahi-daemon start; service mdns start; cat /proc/net/udp | grep -i :14E9')
 
     def start_ot_ctl(self):