[WIRELESS]: Refactor wireless Kconfig.

This patch refactors the wireless Kconfig all over and already
introduces net/wireless/Kconfig with just the WEXT bit for now,
the cfg80211 patch will add to that as well.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>