This avoids getting stuck in state where wpa_supplicant has canceled scans,
but the driver is actually in disassociated state. The previously used code
that controlled scan timeout from WPA module is not really needed anymore
(and has not been needed for past four years since authentication timeout
was separated from scan request timeout), so this can simply be removed to
resolved the race condition. As an extra bonus, this simplifies the
interface to WPA module.
[Bug 261]
