wifi: mac80211: track MU-MIMO configuration on disabled interfaces

wifi: mac80211: track MU-MIMO configuration on disabled interfaces

For monitoring, userspace will try to configure the VIF sdata, while the
driver may see the monitor_sdata that is created when only monitor
interfaces are up. This causes the odd situation that it may not be
possible to store the MU-MIMO configuration on monitor_sdata.

Fix this by storing that information on the VIF sdata and updating the
monitor_sdata when available and the interface is up. Also, adjust the
code that adds monitor_sdata so that it will configure MU-MIMO based on
the newly added interface or one of the existing ones.

This should give a mostly consistent behaviour when configuring MU-MIMO
on sniffer interfaces. Should the user configure MU-MIMO on multiple
sniffer interfaces, then mac80211 will simply select one of the
configurations. This behaviour should be good enough and avoids breaking
user expectations in the common scenarios.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20251110141514.677915f8f6bb.If4e04a57052f9ca763562a67248b06fd80d0c2c1@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>