During MLO roaming, mac80211 may request key removal after the link state
has already been torn down. The current code returns -EINVAL when
link_conf, mconf, or mlink is NULL, causing 'failed to remove key from
hardware (-22)' errors in the kernel log.

This is a race condition where:
1. MLO link teardown begins, cleaning up driver state
2. mac80211 requests group key removal for the old link
3. mt792x_vif_to_bss_conf() or related functions return NULL
4. Driver returns -EINVAL, confusing upper layers

Observed kernel log errors during roaming:
  wlp192s0: failed to remove key (1, ff:ff:ff:ff:ff:ff) from hardware (-22)
  wlp192s0: failed to remove key (4, ff:ff:ff:ff:ff:ff) from hardware (-22)

And associated wpa_supplicant warnings:
  nl80211: kernel reports: link ID must for MLO group key

The fix: When removing a key (cmd != SET_KEY), if the link state is
already gone, return success (0) instead of error. The key is effectively
removed when the link was torn down.

Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Reported-by: Zac Bowling <zac@zacbowling.com>
Tested-by: Zac Bowling <zac@zacbowling.com>
Signed-off-by: Zac Bowling <zac@zacbowling.com>
---
 drivers/net/wireless/mediatek/mt76/mt7925/main.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7925/main.c b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
index 852cf8ff842f..7cf6faa1f6f4 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7925/main.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7925/main.c
@@ -605,8 +605,15 @@ static int mt7925_set_link_key(struct ieee80211_hw *hw, enum set_key_cmd cmd,
 	mconf = mt792x_vif_to_link(mvif, link_id);
 	mlink = mt792x_sta_to_link(msta, link_id);
 
-	if (!link_conf || !mconf || !mlink)
+	if (!link_conf || !mconf || !mlink) {
+		/* During MLO roaming, link state may be torn down before
+		 * mac80211 requests key removal. If removing a key and
+		 * the link is already gone, consider it successfully removed.
+		 */
+		if (cmd != SET_KEY)
+			return 0;
 		return -EINVAL;
+	}
 
 	wcid = &mlink->wcid;
 	wcid_keyidx = &wcid->hw_key_idx;
-- 
2.51.0