staging: wfx: fix case where AP stop with CAB traffic pending

When driver has Content After DTIM Beacon (CAB) in queue, it wait for an
indication from the firmware. However, when we stop to send beacons,
this indication may never happen.

Solve this issue by simply simulate this indication. Firmware will send
data that probably nobody will heard.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200401110405.80282-32-Jerome.Pouiller@silabs.com


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