tests: Make rrm_reassociation more robust

Flush cfg80211 scan cache explicitly when running this test case to
avoid issues with the ROAM command not working due to a scan result from
an earlier test case. This was causing failures in the following test
case sequence:
rrm_beacon_req_active_ap_channels rrm_reassociation

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

tests/hwsim/test_rrm.py

@@ -2096,6 +2096,7 @@ def test_rrm_reassociation(dev, apdev):
     bssid = hapd.own_addr()
 
     addr = dev[0].own_addr()
+    dev[0].flush_scan_cache()
     dev[0].connect("rrm", key_mgmt="NONE", scan_freq="2412")
     check_beacon_req(hapd, addr, 1)