Add a per-game option to turn off wifi

[alemercu]

Is your feature request related to a problem? Please describe.
In Twilight menu on DSi, in settings you can only turn wifi on or off, but a lot of games don't use wifi so it's just a waste of battery %.

Describe the solution you'd like
If possible i suggest to add a new option in per-game settings to choose whether to leave wifi on or off while playing that specific game, so you can leave wifi off for games that don't use it.