Support overclocking and underclocking the Gamecube CPU

Won't work with all games, but provides a nice way to spend extra CPU to make
a variable framerate game faster (e.g. Spyro or The Last Story), or to make
a game use less CPU at the cost of a lower framerate (e.g. Rogue Leader).

Source/Core/Core/NetPlayProto.h

@@ -16,6 +16,8 @@ struct NetSettings
 	bool m_DSPHLE;
 	bool m_DSPEnableJIT;
 	bool m_WriteToMemcard;
+	bool m_OCEnable;
+	float m_OCFactor;
 	TEXIDevices m_EXIDevice[2];
 };