tests: Run dump_monitor() again if scan was pending

tests: Run dump_monitor() again if scan was pending

In addition to running the FLUSH command again, the pending monitor
interface events need be cleared in case the driver was running a scan
when reset() is called. This avoids issues, e.g., with discovery_dev_id
failing due to an unexpected P2P-DEVICE-FOUND event that was generated
by the pending scan operation that had not yet complete when the first
dump_monitor() call in reset() happened.

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