package/wpa_supplicant: Enable support for log to debug file

Enable the '-f' option (log output to debug file instead of stdout). Force
enable it, binary size +963 bytes for an ARM target.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Acked-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>