Allow WPA passphrase to be fetched with RADIUS Tunnel-Password attribute

Allow WPA passphrase to be fetched with RADIUS Tunnel-Password attribute

This allows per-device PSK to be configured for WPA-Personal using a
RADIUS authentication server. This uses RADIUS-based MAC address ACL
(macaddr_acl=2), i.e., Access-Request uses the MAC address of the
station as the User-Name and User-Password. The WPA passphrase is
returned in Tunnel-Password attribute in Access-Accept. This
functionality can be enabled with the new hostapd.conf parameter,
wpa_psk_radius.

Signed-hostap: Michael Braun <michael-dev@fami-braun.de>