libcamera: object: Make message() method protected

The message() method shouldn't be called externally (except by a few
friend classes), make it protected.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

include/libcamera/object.h

@@ -26,11 +26,13 @@ public:
 	virtual ~Object();
 
 	void postMessage(std::unique_ptr<Message> msg);
-	virtual void message(Message *msg);
 
 	Thread *thread() const { return thread_; }
 	void moveToThread(Thread *thread);
 
+protected:
+	virtual void message(Message *msg);
+
 private:
 	template<typename... Args>
 	friend class Signal;