wpa: Address CTRL-EVENT-SCAN-FAILED

5fcdc19a8111 didn't fully resolve the issue. There remains a report
that an ifconfig wlan0 up by itself is insufficient. Ifconfig down
must precede it.

Reported by: Filipe da Silva Santos <contact _ shiori_com_br>
Fixes: 5fcdc19a8111
MFC after: 3 days