Add automatic scanning support

Add automatic scanning support

Like bgscan, autoscan is an optional module based feature to automate
scanning but while disconnected or inactive.

Instead of requesting directly a scan, it only sets the scan_interval
and the sched_scan_interval. So, if the driver supports sched_scan,
autoscan will be able to tweak its interval. Otherwise, the tweaked
scan_interval will be used. If scan parameters needs to be tweaked, an
autoscan_params pointer in wpa_s will provide those. So req_scan /
req_sched_scan will not set the scan parameters as they usually do, but
instead will use this pointer.

Modules will not have to request a scan directly, like bgscan does.
Instead, it will need to return the interval it wants after each
notification.

Signed-hostap: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>