mac80211: refactor the scan code

Move the processing of each scan state into its own functions for better
readability. This patch does not introduce functional changes.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>