The scan path to initiate another scan if the initial association failed
was broken due to wpa_s->scan_req being zeroed earlier in
wpa_supplicant_scan(). This caused the second scan to bail out early
since it thought this was not a requested scan.
In situations where the driver does background scanning and sends a
steady stream of scan results, wpa_supplicant would continually
reschedule the scan. This resulted in specific SSID scans never
happening for a hidden AP, and the supplicant never connecting to the AP
because it never got found. Instead, if there's an already scheduled
scan, and a request comes in to reschedule it, and there are enabled
scan_ssid=1 network blocks, let the scan happen anyway so the hidden
SSID has a chance to be found.
