Retry scan-for-connect if driver trigger fails

Retry scan-for-connect if driver trigger fails

This restores some of the pre-radio work behavior for scanning by
retrying scan trigger if the driver rejects it (most likely returning
EBUSY in case of nl80211-drivers). Retry is indicated in the
CTRL-EVENT-SCAN-FAILED event with "retry=1".

For manual scans (e.g., triggered through "SCAN" control interface
command), no additional retries are performed. In other words, if upper
layers want to retry, they can do so based on the CTRL-EVENT-SCAN-FAILED
event.

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