nl80211: Event notifications for MLME events

Add new nl80211 event notifications (and a new multicast group, "mlme")
for informing user space about received and processed Authentication,
(Re)Association Response, Deauthentication, and Disassociation frames in
station and IBSS modes (i.e., MLME SAP interface primitives
MLME-AUTHENTICATE.confirm, MLME-ASSOCIATE.confirm,
MLME-REASSOCIATE.confirm, MLME-DEAUTHENTICATE.indicate, and
MLME-DISASSOCIATE.indication). The event data is encapsulated as the 802.11
management frame since we already have the frame in that format and it
includes all the needed information.

This is the initial step in providing MLME SAP interface for
authentication and association with nl80211. In other words, kernel code
will act as the MLME and a user space application can control it as the
SME.

Signed-off-by: Jouni Malinen <j@w1.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>