mac80211: reorder MLME code more

This way all the utility functions are at the top, then the
state machine and externally callable functions are moved to
the bottom. Also clean up ieee80211_i.h a bit and add a few
comments about which functions are called from where.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>