wifi: wireless: deny wireless extensions on MLO-capable devices

These are WiFi 7 devices that will be introduced into the market
in 2023, with new drivers. Wireless extensions haven't been in
real development since 2006. Since wireless has evolved a lot,
and continues to evolve significantly with Multi-Link Operation,
there's really no good way to still support wireless extensions
for devices that do MLO.

Stop supporting wireless extensions for new devices. We don't
consider this a regression since no such devices (apart from
hwsim) exist yet.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230118105152.45f85078a1e0.Ib9eabc2ec5bf6b0244e4d973e93baaa3d8c91bd8@changeid

net/wireless/wext-core.c

@@ -662,6 +662,8 @@ struct iw_statistics *get_wireless_stats(struct net_device *dev)
 	    dev->ieee80211_ptr->wiphy->wext &&
 	    dev->ieee80211_ptr->wiphy->wext->get_wireless_stats) {
 		wireless_warn_cfg80211_wext();
+		if (dev->ieee80211_ptr->wiphy->flags & WIPHY_FLAG_SUPPORTS_MLO)
+			return NULL;
 		return dev->ieee80211_ptr->wiphy->wext->get_wireless_stats(dev);
 	}
 #endif
@@ -702,6 +704,8 @@ static iw_handler get_handler(struct net_device *dev, unsigned int cmd)
 #ifdef CONFIG_CFG80211_WEXT
 	if (dev->ieee80211_ptr && dev->ieee80211_ptr->wiphy) {
 		wireless_warn_cfg80211_wext();
+		if (dev->ieee80211_ptr->wiphy->flags & WIPHY_FLAG_SUPPORTS_MLO)
+			return NULL;
 		handlers = dev->ieee80211_ptr->wiphy->wext;
 	}
 #endif