net: add forgotten IFF_L3MDEV_SLAVE define

Fixes: fee6d4c77 ("net: Add netif_is_l3_slave")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed