mac80211: Add support for declaring MU-MIMO capability

Add support for declaring MU-MIMO beamformee capability for
relevant hardware.
When sending association request, the capability is included if both
hardware and the AP support it, and no other virtual interface
is using it.
This is in order to avoid multiple interfaces using MU-MIMO in parallel
which might lead to contradictions in the group-id mechanism.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ieee80211_i.h

@@ -721,6 +721,7 @@ struct ieee80211_if_mesh {
  *	back to wireless media and to the local net stack.
  * @IEEE80211_SDATA_DISCONNECT_RESUME: Disconnect after resume.
  * @IEEE80211_SDATA_IN_DRIVER: indicates interface was added to driver
+ * @IEEE80211_SDATA_MU_MIMO_OWNER: indicates interface owns MU-MIMO capability
  */
 enum ieee80211_sub_if_data_flags {
 	IEEE80211_SDATA_ALLMULTI		= BIT(0),
@@ -728,6 +729,7 @@ enum ieee80211_sub_if_data_flags {
 	IEEE80211_SDATA_DONT_BRIDGE_PACKETS	= BIT(3),
 	IEEE80211_SDATA_DISCONNECT_RESUME	= BIT(4),
 	IEEE80211_SDATA_IN_DRIVER		= BIT(5),
+	IEEE80211_SDATA_MU_MIMO_OWNER		= BIT(6),
 };
 
 /**