The user space can now allow the kernel to associate to an AP that
requires MFP or that doesn't have MFP enabled in the same
NL80211_CMD_CONNECT command, by using a new NL80211_MFP_OPTIONAL flag.
The driver / firmware will decide whether to use it or not.

Include a feature bit to advertise support for NL80211_MFP_OPTIONAL.
This allows new user space to run on old kernels and know that it
cannot use the new attribute if it isn't supported.
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>