MXS-1220: Add old router diagnostic interface

Added back the old diagnostic entry point to the router interface.

server/modules/routing/schemarouter/schemarouterinstance.hh

@@ -37,7 +37,8 @@ public:
     ~SchemaRouter();
     static SchemaRouter* create(SERVICE* pService, char** pzOptions);
     SchemaRouterSession* newSession(MXS_SESSION* pSession);
-    json_t* diagnostics() const;
+    void diagnostics(DCB* pDcb);
+    json_t* diagnostics_json() const;
     uint64_t getCapabilities();
 
 private: