tests: Make discovery_auto more robust

This test case could fail if there were old BSS entries remaining in
cfg80211 scan results. That happened, e.g., when running test cases in
the following sequence: "discovery_social_plus_one discovery_auto".

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

tests/hwsim/test_p2p_discovery.py

@@ -289,6 +289,7 @@ def test_discovery_and_interface_disabled(dev):
 
 def test_discovery_auto(dev):
     """P2P device discovery and provision discovery with auto GO/dev selection"""
+    dev[0].flush_scan_cache()
     addr0 = dev[0].p2p_dev_addr()
     addr1 = dev[1].p2p_dev_addr()
     addr2 = dev[2].p2p_dev_addr()