wifi: mac80211: add MLO link ID to TX frame metadata

Take a few bits out of the control.flags to add the link ID
to TX frame metadata, so drivers don't need to look it up
by the address themselves. Implement that lookup where it's
needed, for internal frame TX, and set it to "unspecified"
for data transmissions.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/mac80211.h

@@ -867,6 +867,10 @@ enum mac80211_tx_info_flags {
  * @IEEE80211_TX_CTRL_DONT_REORDER: This frame should not be reordered
  *	relative to other frames that have this flag set, independent
  *	of their QoS TID or other priority field values.
+ * @IEEE80211_TX_CTRL_MLO_LINK: If not @IEEE80211_LINK_UNSPECIFIED, this
+ *	frame should be transmitted on the specific link. This really is
+ *	only relevant for frames that do not have data present, and is
+ *	also not used for 802.3 format frames.
  *
  * These flags are used in tx_info->control.flags.
  */
@@ -880,8 +884,11 @@ enum mac80211_tx_control_flags {
 	IEEE80211_TX_INTCFL_NEED_TXPROCESSING	= BIT(6),
 	IEEE80211_TX_CTRL_NO_SEQNO		= BIT(7),
 	IEEE80211_TX_CTRL_DONT_REORDER		= BIT(8),
+	IEEE80211_TX_CTRL_MLO_LINK		= 0xf0000000,
 };
 
+#define IEEE80211_LINK_UNSPECIFIED	0xf
+
 /**
  * enum mac80211_tx_status_flags - flags to describe transmit status
  *