nl80211/cfg80211: Set Operating Mode Notification

This attribute is needed for setting Operating Mode Notification
in AP mode from User Space. This functionality is required when
User Space received Assoc Request contains Operation Mode
Notification element.

Signed-off-by: Marek Kwaczynski <marek.kwaczynski@tieto.com>
[fix typos, nl80211 documentation]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>