staging: wfx: avoid possible lock-up during scan

If the environment is noisy, the device may take time to send scan
requests. Thus, scan requests durations > 5s have already been observed.
During the scan, traffic is neither received, neither sent. From the
user point-of-view, the traffic is frozen for a long time.

This patch reworks the scan processing. It gives to the device a smaller
time budget than previously. However, it does not expect the scan to be
complete and it is able to send another scan request to finish the work.

A big part of the patch aims to avoid an infinite loop if the device
goes crazy.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20210913130203.1903622-6-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>