cfg80211/mac80211: allow action frame TX/RX in IBSS

When in IBSS mode, currently action frame TX and RX
cannot be used. Allow using it to talk to any peer,
or for public action frames. Also, while at it,
restructure the code in mac80211 to make it easier
to add this for other interface types in the future.

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