tests: Clear pending monitor events before starting scan

The wait_event() call for scan completion could have processed a
previously received event from a prior scan instead of the newly started
one. This could result in flush_scan_cache() assuming there are still
results in the cache even though the scan request to clear the cache had
not even be started yet.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

tests/hwsim/wpasupplicant.py

@@ -1050,6 +1050,8 @@ class WpaSupplicant:
 
     def scan(self, type=None, freq=None, no_wait=False, only_new=False,
              passive=False):
+        if not no_wait:
+            self.dump_monitor()
         if type:
             cmd = "SCAN TYPE=" + type
         else: