It was possible for the hidden SSID entry to leak into following test
cases and result in failures, e.g., in this sequence:
scan_hidden
scan_reqs_with_non_scan_radio_work
radius_auth_unreachable
wep_open_auth
BSS <BSSID> picked incorrect BSS entry within wpa_supplicant due to the
old zero-length SSID showing up from the earlier hidden SSID case.
Signed-off-by: Jouni Malinen <j@w1.fi>