tests: More thorough cache clearing in ap_hs20_hidden_ssid_in_scan_res

It looked like cfg80211 BSS entry for the zero-length SSID could remain
after this test case. Stop the AP and scan twice with flush-cache option
to make this less likely to occur and cause issues to following test
cases.

Signed-off-by: Jouni Malinen <j@w1.fi>
1 file changed