net: ieee802154: stop dump llsec devkeys for monitors

This patch stops dumping llsec devkeys 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/20210405003054.256017-10-aahringo@redhat.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

net/ieee802154/nl802154.c

@@ -1853,6 +1853,11 @@ nl802154_dump_llsec_devkey(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;