Switch instanceName used in FindCommissionableNode (backport #71877)

src/controller/CHIPDeviceController.cpp

@@ -1912,7 +1912,7 @@ CHIP_ERROR DeviceCommissioner::SetUdcListenPort(uint16_t listenPort)
     return CHIP_NO_ERROR;
 }
 
-void DeviceCommissioner::FindCommissionableNode(char * instanceName)
+void DeviceCommissioner::FindCommissionableNode(const char * instanceName)
 {
     Dnssd::DiscoveryFilter filter(Dnssd::DiscoveryFilterType::kInstanceName, instanceName);
     DiscoverCommissionableNodes(filter);

src/controller/CHIPDeviceController.h

@@ -784,7 +784,7 @@ class DLL_EXPORT DeviceCommissioner : public DeviceController,
      * @param instanceName DNS-SD instance name for the client requesting commissioning
      *
      */
-    void FindCommissionableNode(char * instanceName) override;
+    void FindCommissionableNode(const char * instanceName) override;
 
     /**
      * @brief

src/protocols/user_directed_commissioning/UserDirectedCommissioning.h

@@ -454,7 +454,7 @@ class DLL_EXPORT InstanceNameResolver
      * @param instanceName DNS-SD instance name for the client requesting commissioning
      *
      */
-    virtual void FindCommissionableNode(char * instanceName) = 0;
+    virtual void FindCommissionableNode(const char * instanceName) = 0;
 
     virtual ~InstanceNameResolver() = default;
 };

src/protocols/user_directed_commissioning/UserDirectedCommissioningServer.cpp

@@ -120,7 +120,7 @@ void UserDirectedCommissioningServer::HandleNewUDC(const Transport::PeerAddress
         // Call the registered InstanceNameResolver, if any.
         if (mInstanceNameResolver != nullptr)
         {
-            mInstanceNameResolver->FindCommissionableNode(instanceName);
+            mInstanceNameResolver->FindCommissionableNode(client->GetInstanceName());
         }
         else
         {

src/protocols/user_directed_commissioning/tests/TestUdcMessages.cpp

@@ -47,15 +47,15 @@ class DLL_EXPORT TestCallback : public UserConfirmationProvider, public Instance
 
     void OnCommissionerPasscodeReady(UDCClientState state) {}
 
-    void FindCommissionableNode(char * instanceName)
+    void FindCommissionableNode(const char * instanceName)
     {
         mFindCommissionableNodeCalled = true;
         mInstanceName                 = instanceName;
     }
 
     // virtual ~UserConfirmationProvider() = default;
     UDCClientState mState;
-    char * mInstanceName;
+    const char * mInstanceName = nullptr;
 
     bool mOnUserDirectedCommissioningRequestCalled = false;
     bool mFindCommissionableNodeCalled             = false;