ipw2200: select CFG80211_WEXT

Commit 24a0aa21 ("cfg80211: make WEXT compatibility unselectable")
made it impossible to depend on CFG80211_WEXT. It does still allow to
select that symbol. (Yes, the commit summary is confusing.)

So make IPW2200 select CFG80211_WEXT, so that the ipw2200 driver can be
enabled in config again.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>