WX: Add menu item to perform system update from disc

Source/Core/DolphinWX/Frame.h

@@ -347,6 +347,7 @@ private:
   void OnImportBootMiiBackup(wxCommandEvent& event);
   void OnExtractCertificates(wxCommandEvent& event);
   void OnPerformOnlineWiiUpdate(wxCommandEvent& event);
+  void OnPerformDiscWiiUpdate(wxCommandEvent& event);
   void OnFifoPlayer(wxCommandEvent& event);
   void OnConnectWiimote(wxCommandEvent& event);
   void GameListChanged(wxCommandEvent& event);