tests: Make DPP relay tests more robust

Flush scan results to avoid failure caused by incorrect channel
selection based on an old result for the same BSSID. This was found with
the following test sequence:
ap_track_sta_no_auth dpp_network_intro_version_missing_req dpp_controller_relay_pkex

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

tests/hwsim/test_dpp.py

@@ -5406,6 +5406,8 @@ def run_dpp_controller_relay(dev, apdev, params, chirp=False):
     wait_auth_success(relay, dev[1], configurator=dev[1], enrollee=relay)
     update_hapd_config(relay)
 
+    dev[0].flush_scan_cache()
+
     # Initiate from Enrollee with broadcast DPP Authentication Request or
     # using chirping
     dev[0].set("dpp_config_processing", "2")

tests/hwsim/test_dpp3.py

@@ -260,6 +260,8 @@ def run_dpp_controller_relay_pkex(dev, apdev, params):
     if "FAIL" in res:
         raise Exception("Failed to set PKEX data (Controller)")
 
+    dev[0].flush_scan_cache()
+
     # Initiate PKEX from Enrollee
     dev[0].set("dpp_config_processing", "2")
     dev[0].dpp_pkex_init(identifier=None, code=code, role="enrollee")