nl80211: advertise device AP SME

Add the ability to advertise that the device
contains the AP SME and what features it can
support. There are currently no features in
the bitmap -- probe response offload will be
advertised by a few patches Arik is working
on now (who took over from Guy Eilam) and a
device with AP SME will typically implement
and require response offload.

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