ieee80211: introduce Self Protected Action codes

802.11s introduces a new action frame category, add action codes as well
as an entry in ieee80211_mgmt.

Signed-off-by: Thomas Pedersen <thomas@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>