wifi: iwlwifi: mvm: track AP STA pointer and use it for MFP

wifi: iwlwifi: mvm: track AP STA pointer and use it for MFP

Instead of relying on the AP STA ID and dereferencing our
firmware -> mac80211 STA array when we really only need
the STA, not the per-link information (and might not have
it, e.g. for a pairwise key installation where this is
relevant), keep track of the AP STA as a pointer to the
mac80211 STA, protected by the mutex. Then use it here in
the key code instead.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230414130637.7db01b1508de.I88e6d252cdb0a6e4581d7c5fd7cbc037b4fd40ae@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>