[ncp] add empty implementation for dnssd platform APIs (#10877)

This commit adds empty implementation for a NCP based version of
otPlatDnssd APIs.

Like NCP version of otPlatInfraIf APIs, this commit adds a control
option to enable/disable the simulation platform version of
otPlatDnssd APIs to avoid conflict. By default, the simulation version
of implementation will still be turned on.

examples/platforms/simulation/CMakeLists.txt

@@ -52,6 +52,13 @@ else()
     target_compile_definitions(ot-simulation-config INTERFACE "OPENTHREAD_SIMULATION_IMPLEMENT_INFRA_IF=0")
 endif()
 
+option(OT_SIMULATION_DNSSD "enable simulation dnssd" ON)
+if (OT_SIMULATION_DNSSD)
+    target_compile_definitions(ot-simulation-config INTERFACE "OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD=1")
+else()
+    target_compile_definitions(ot-simulation-config INTERFACE "OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD=0")
+endif()
+
 if(NOT OT_PLATFORM_CONFIG)
     set(OT_PLATFORM_CONFIG "openthread-core-simulation-config.h" PARENT_SCOPE)
 endif()

examples/platforms/simulation/dnssd.c

@@ -30,7 +30,7 @@
 
 #include <openthread/platform/dnssd.h>
 
-#if OPENTHREAD_CONFIG_PLATFORM_DNSSD_ENABLE
+#if OPENTHREAD_CONFIG_PLATFORM_DNSSD_ENABLE && OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD
 otPlatDnssdState otPlatDnssdGetState(otInstance *aInstance)
 {
     OT_UNUSED_VARIABLE(aInstance);
@@ -164,4 +164,4 @@ void otPlatDnssdStopIp4AddressResolver(otInstance *aInstance, const otPlatDnssdA
     OT_UNUSED_VARIABLE(aResolver);
 }
 
-#endif // OPENTHREAD_CONFIG_PLATFORM_DNSSD_ENABLE
+#endif // OPENTHREAD_CONFIG_PLATFORM_DNSSD_ENABLE && OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD

examples/platforms/simulation/platform-config.h

@@ -116,3 +116,12 @@
 #ifndef OPENTHREAD_SIMULATION_IMPLEMENT_INFRA_IF
 #define OPENTHREAD_SIMULATION_IMPLEMENT_INFRA_IF 1
 #endif
+
+/**
+ * @def OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD
+ *
+ * Define as 1 for the simulation platform to provide implementation of `otPlatDnssd` APIs.
+ */
+#ifndef OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD
+#define OPENTHREAD_SIMULATION_IMPLEMENT_DNSSD 1
+#endif