net: introduce IFF_UNICAST_FLT private flag

Use IFF_UNICAST_FTL to find out if driver handles unicast address
filtering. In case it does not, promisc mode is entered.

Patch also fixes following drivers:
stmmac, niu: support uc filtering and yet it propagated
	ndo_set_multicast_list
bna, benet, pxa168_eth, ks8851, ks8851_mll, ksz884x : has set
	ndo_set_rx_mode but do not support uc filtering

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0c7321c..4f09f88 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -949,6 +949,7 @@
 		return -ENOMEM;
 
 	/* Set up network device as normal. */
+	dev->priv_flags |= IFF_UNICAST_FLT;
 	dev->netdev_ops = &virtnet_netdev;
 	dev->features = NETIF_F_HIGHDMA;