EXI_Device: Always define EXIDEVICE_ETHTAPSERVER for consistency

This keeps the enum values consistent across platforms in case new
entries are added after EXIDEVICE_ETHTAPSERVER.

Source/Core/Core/HW/EXI/EXI_Device.h

@@ -33,9 +33,8 @@ enum TEXIDevices : int
   EXIDEVICE_MEMORYCARDFOLDER,
   EXIDEVICE_AGP,
   EXIDEVICE_ETHXLINK,
-#if defined(__APPLE__)
+  // Only used on Apple devices.
   EXIDEVICE_ETHTAPSERVER,
-#endif
   EXIDEVICE_NONE = 0xFF
 };