net: add forgotten IFF_L3MDEV_SLAVE define

Fixes: fee6d4c7 ("net: Add netif_is_l3_slave")
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Acked-by: NDavid Ahern <dsa@cumulusnetworks.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1322,6 +1322,7 @@ enum netdev_priv_flags {
 #define IFF_L3MDEV_MASTER		IFF_L3MDEV_MASTER
 #define IFF_NO_QUEUE			IFF_NO_QUEUE
 #define IFF_OPENVSWITCH			IFF_OPENVSWITCH
+#define IFF_L3MDEV_SLAVE		IFF_L3MDEV_SLAVE
 
 /**
  *	struct net_device - The DEVICE structure.