wifi: mac80211: report per-link error during association

With this cfg80211 can report the link that caused the error to
userspace which is then able to react to it by e.g. removing the link
from the association and retrying.

Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230920211508.275fc7f5c426.I8086c0fdbbf92537d6a8b8e80b33387fcfd5553d@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -7866,8 +7866,10 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 		/* only calculate the flags, hence link == NULL */
 		err = ieee80211_prep_channel(sdata, NULL, assoc_data->link[i].bss,
 					     &assoc_data->link[i].conn_flags);
-		if (err)
+		if (err) {
+			req->links[i].error = err;
 			goto err_clear;
+		}
 	}
 
 	/* needed for transmitting the assoc frames properly */