wifi: iwlwifi: mvm: validate station properly in flush

wifi: iwlwifi: mvm: validate station properly in flush

If we have MLO, then the deflink.ap_sta_id cannot be used.
However, we can use the new mvmvif->ap_sta pointer for the
validation instead.

Also don't do it multiple times for different FW instances
of the same AP STA (TDLS STAs are only on a single link).

Note that this isn't really working right yet since the
underlying flush code hasn't been updated yet to know of
multiple link STAs.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230414130637.7d747df44d65.Ie5392859fab4cfb73c20b49bfee2caadef5fd8ec@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>