Allow settings to be marked as readonly

In the case of the FIRE 2 ethernet, we're waiting on a bug fix in firmware before we re-enable writing.
In the meantime, setting settings over ethernet crashes the ethernet driver.

device/include/idevicesettings.h

@@ -302,6 +302,8 @@ public:
 	template<typename T> bool setStructure(const T& newStructure);
 
 	uint8_t getEnumValueForBaudrate(uint32_t baudrate);
+
+	bool readonly = false;
 protected:
 	std::shared_ptr<Communication> com;
 	size_t structSize;