net: ieee802154: stop dump llsec seclevels for monitors

This patch stops dumping llsec seclevels for monitors which we don't
support yet. Otherwise we will access llsec mib which isn't initialized
for monitors.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210405003054.256017-13-aahringo@redhat.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

net/ieee802154/nl802154.c

@@ -2026,6 +2026,11 @@ nl802154_dump_llsec_seclevel(struct sk_buff *skb, struct netlink_callback *cb)
 	if (err)
 		return err;
 
+	if (wpan_dev->iftype == NL802154_IFTYPE_MONITOR) {
+		err = skb->len;
+		goto out_err;
+	}
+
 	if (!wpan_dev->netdev) {
 		err = -EINVAL;
 		goto out_err;