nl80211 : Add support for configuring MFP

nl80211 : Add support for configuring MFP

NL80211_CMD_ASSOCIATE request must be able to indicate whether
management frame protection (IEEE 802.11w) is being used. mac80211 was
able to use MFP in client mode only with WEXT, but the new
NL80211_ATTR_USE_MFP attribute will allow this to be done with
nl80211, too.

Since we are currently using nl80211 for MFP only with drivers that
use user space SME, only MFP disabled and required values are
used. However, the NL80211_ATTR_USE_MFP attribute is an enum that can
be extended with MFP optional in the future, if that is needed with
some drivers (e.g., if the RSN IE is generated by the driver).

Signed-off-by: Jouni Malinen <jouni.malinen@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>