iwlwifi: mvm: Use the AP station for non_sta transmit

In iwl_mvm_tx_skb_non_sta(), in case of managed interface,
use the AP station for multicast frames instead of the auxiliary
station as otherwise the frames can be sent to an absent P2P GO as
the FW does not block transmissions for the auxiliary station
since it is not associated with the station MAC context.

Note that this is not possible for unicast frames, as a TDLS
discovery response is sent without a station entry, and in this
case the P2P GO NoA should not block transmission to the peer.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>