D-Bus: Set last_scan_req to MANUAL_SCAN_REQ on Scan() trigger paths

D-Bus: Set last_scan_req to MANUAL_SCAN_REQ on Scan() trigger paths

The D-Bus Scan() handler was setting wpa_s->scan_req = MANUAL_SCAN_REQ
on the code path that used wpa_supplicant_req_scan(). However, it did
not do anything similar for the cases where
wpa_supplicant_trigger_scan() is called directly. This could result in
unexpected wpa_s->last_scan_req value and incorrect behavior especially
when using ap_scan=2 and running a scan while operating in AP mode. Fix
this by explicitly setting wpa_s->last_scan_req = MANUAL_SCAN_REQ when
using wpa_supplicant_trigger_scan() from the Scan() handler.

Signed-off-by: Jouni Malinen <j@w1.fi>