WNM: Clean up old scan data processing

WNM: Clean up old scan data processing

When receiving a BTM request, wpa_supplicant would try to fetch new
results from the driver, and, independently of that, would also process
the latest scan results that were partially updated by the previous
fetch.

Simplify the logic by using wpa_supplicant_get_scan_results() directly
and then process the old scan data as usual. However, this data may be
outdated, so add a new heuristic to avoid roaming to a BSS if it is
either outdated or bad.

Doing this moves all scan data processing into wnm_scan_process() and
removes duplicated functionality for scan result processing in scan.c.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>