stop gcc complaints about func ptr conversions

src/csharp/ext/grpc_csharp_ext.c

@@ -906,24 +906,26 @@ GPR_EXPORT grpc_credentials *GPR_CALLTYPE grpcsharp_composite_credentials_create
 /* Metadata credentials plugin */
 
 GPR_EXPORT void GPR_CALLTYPE grpcsharp_metadata_credentials_notify_from_plugin(
-	void *callback_ptr, void *user_data, grpc_metadata_array *metadata,
+    grpc_credentials_plugin_metadata_cb cb,
+    void *user_data, grpc_metadata_array *metadata,
   grpc_status_code status, const char *error_details) {
-	grpc_credentials_plugin_metadata_cb cb = (grpc_credentials_plugin_metadata_cb)callback_ptr;
   cb(user_data, metadata->metadata, metadata->count, status, error_details);
 }
 
 typedef void(GPR_CALLTYPE *grpcsharp_metadata_interceptor_func)(
-	void *state, const char *service_url, void *callback_ptr,
+  void *state, const char *service_url, grpc_credentials_plugin_metadata_cb cb,
   void *user_data, gpr_int32 is_destroy);
 
 static void grpcsharp_get_metadata_handler(void *state, const char *service_url,
   grpc_credentials_plugin_metadata_cb cb, void *user_data) {
-	grpcsharp_metadata_interceptor_func interceptor = (grpcsharp_metadata_interceptor_func)state;
-	interceptor(state, service_url, (void*)cb, user_data, 0);
+  grpcsharp_metadata_interceptor_func interceptor =
+      (grpcsharp_metadata_interceptor_func)(gpr_intptr)state;
+  interceptor(state, service_url, cb, user_data, 0);
 }
 
 static void grpcsharp_metadata_credentials_destroy_handler(void *state) {
-	grpcsharp_metadata_interceptor_func interceptor = (grpcsharp_metadata_interceptor_func)state;
+  grpcsharp_metadata_interceptor_func interceptor =
+      (grpcsharp_metadata_interceptor_func)(gpr_intptr)state;
   interceptor(state, NULL, NULL, NULL, 1);
 }
 
@@ -932,7 +934,7 @@ GPR_EXPORT grpc_credentials *GPR_CALLTYPE grpcsharp_metadata_credentials_create_
   grpc_metadata_credentials_plugin plugin;
   plugin.get_metadata = grpcsharp_get_metadata_handler;
   plugin.destroy = grpcsharp_metadata_credentials_destroy_handler;
-  plugin.state = metadata_interceptor;
+  plugin.state = (void*)(gpr_intptr)metadata_interceptor;
   return grpc_metadata_credentials_create_from_plugin(plugin, NULL);
 }