mac80211: implement nan_change_conf

Implement nan_change_conf callback which allows to change current
NAN configuration (master preference and dual band operation).
Store the current NAN configuration in sdata, so it can be used
both to provide the driver the updated configuration with changes
and also it will be used in hw reconfig flows in next patches.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
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>