ieee80211: convert defines to enums

From: Gertjan van Wingerde <gwingerde@home.nl>

Attached patch cleans up the long lists of #defines for status codes,
reason codes, and information elements.

Signed-off-by: Gertjan van Wingerde <gwingerde@home.nl>
Signed-off-by: Jiri Benc <jbenc@suse.cz>