6lowpan: Only make 6lowpan links to IEEE802154 devices

Refuse to create 6lowpan links if the actual hardware interface is
of any type other than ARPHRD_IEEE802154.

Signed-off-by: Alan Ott <alan@signal11.us>
Suggested-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan.c

@@ -1372,6 +1372,8 @@ static int lowpan_newlink(struct net *src_net, struct net_device *dev,
 	real_dev = dev_get_by_index(src_net, nla_get_u32(tb[IFLA_LINK]));
 	if (!real_dev)
 		return -ENODEV;
+	if (real_dev->type != ARPHRD_IEEE802154)
+		return -EINVAL;
 
 	lowpan_dev_info(dev)->real_dev = real_dev;
 	lowpan_dev_info(dev)->fragment_tag = 0;