wifi: cfg80211: Prevent cfg80211_wext_siwencodeext() on MLD

Currently, MLO support is not added for WEXT code and WEXT handlers are
prevented on MLDs. Prevent WEXT handler cfg80211_wext_siwencodeext()
also on MLD which is missed in commit 7b0a0e3c ("wifi: cfg80211: do
some rework towards MLO link APIs")
Signed-off-by: Veerendranath Jakkam <quic_vjakkam@quicinc.com>
Link: https://lore.kernel.org/r/20220730052643.1959111-3-quic_vjakkam@quicinc.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/wext-compat.c

@@ -685,6 +685,13 @@ static int cfg80211_wext_siwencodeext(struct net_device *dev,
 	    !rdev->ops->set_default_key)
 		return -EOPNOTSUPP;
 
+	wdev_lock(wdev);
+	if (wdev->valid_links) {
+		wdev_unlock(wdev);
+		return -EOPNOTSUPP;
+	}
+	wdev_unlock(wdev);
+
 	switch (ext->alg) {
 	case IW_ENCODE_ALG_NONE:
 		remove = true;