Fix a regression in storing of external_auth SSID/BSSID

Fix a regression in storing of external_auth SSID/BSSID

An earlier change in drivers_ops API for struct external_auth broke the
way SSID and BSSID for an external authentication request were stored.
The implementation depended on the memory array being available in the
API struct with a use of memcpy() to copy the full structure even though
when only SSID and BSSID was needed. Fix this by replacing that
easy-to-break storing mechanism with explicit arrays for the exact set
of needed information.

Fixes: dd1a8cef4c05 ("Remove unnecessary copying of SSID and BSSID for external_auth")
Signed-off-by: Jouni Malinen <j@w1.fi>