iwlagn: fix scan complete processing

When we cancel a scan, the completion runs
only from the workqueue. This can cause the
remain-on-channel scan to fail when another
one was just canceled, because we're still
aborting it.

To fix this, run the completion inline with
the lock still held before returning from
iwl_scan_cancel_timeout().

Also, to avoid the scan complete work from
completing a new scan prematurely, add a
new STATUS_SCAN_COMPLETE bit.

Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>