wireless: default CONFIG_WLAN to y

When this was added no defaults were set and it seems
this implies n. Default this to y.

Reported-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>