[PATCH] wireless/airo: cache wireless scans

Observed problems when multiple processes request scans and subsequently
scan results.  This causes a scan result request to hit card registers
before the scan is complete, returning an incomplete scan list and
possibly making the card very angry.  Instead, cache the results of a
wireless scan and serve result requests from the cache, rather than
hitting the hardware for them.
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>