tests: Make go_neg_forced_freq_diff_than_bss_freq more robust

It was possible for this test case to fail due to PBC overlap that was
detected based on previous test case having used PBC. Make that false
positive less likely to happen by explicitly clearing the scan cache on
the device.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>

tests/hwsim/test_p2p_channel.py

@@ -337,6 +337,10 @@ def test_go_neg_forced_freq_diff_than_bss_freq(dev, apdev):
         if wpas.get_mcc() < 2:
            raise Exception("New radio does not support MCC")
 
+        # Clear possible PBC session overlap from previous test case
+        dev[1].request("BSS_FLUSH 0")
+        dev[1].request("SCAN freq=2412 only_new=1")
+
         wpas.request("SET p2p_no_group_iface 0")
 
         hapd = hostapd.add_ap(apdev[0]['ifname'],