iwlagn: refactor scan complete

We'll need to be able to run scan complete
inline, not from the workqueue, so refactor
it.

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