NetPlay: Implement golf mode

This is an extension of host input authority that allows switching the
host (who has zero latency) on the fly, at the further expense of
everyone else's latency. This is useful for turn-based games where the
latency of players not on their turn doesn't matter.

To become the so-called golfer, the player simply presses a hotkey.
When the host is the golfer, latency is identical to normal host input
authority.

Source/Core/Core/NetPlayProto.h

@@ -83,6 +83,9 @@ struct NetSettings
   std::string m_SaveDataRegion;
   bool m_SyncAllWiiSaves;
   std::array<int, 4> m_WiimoteExtension;
+  bool m_GolfMode;
+
+  // These aren't sent over the network directly
   bool m_IsHosting;
   bool m_HostInputAuthority;
 };
@@ -128,6 +131,12 @@ enum
   NP_MSG_WIIMOTE_DATA = 0x70,
   NP_MSG_WIIMOTE_MAPPING = 0x71,
 
+  NP_MSG_GOLF_REQUEST = 0x90,
+  NP_MSG_GOLF_SWITCH = 0x91,
+  NP_MSG_GOLF_ACQUIRE = 0x92,
+  NP_MSG_GOLF_RELEASE = 0x93,
+  NP_MSG_GOLF_PREPARE = 0x94,
+
   NP_MSG_START_GAME = 0xA0,
   NP_MSG_CHANGE_GAME = 0xA1,
   NP_MSG_STOP_GAME = 0xA2,