af_packet: Teach to listen for multiple unicast addresses.

The the PACKET_ADD_MEMBERSHIP and the PACKET_DROP_MEMBERSHIP setsockopt
calls for af_packet already has all of the infrastructure needed to subscribe
to multiple mac addresses.  All that is missing is a flag to say that
the address we want to listen on is a unicast address.

So introduce PACKET_MR_UNICAST and wire it up to dev_unicast_add and
dev_unicast_delete.

Additionally I noticed that errors from dev_mc_add were not propagated
from packet_dev_mc so fix that.
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if_packet.h

@@ -145,5 +145,6 @@ struct packet_mreq
 #define PACKET_MR_MULTICAST	0
 #define PACKET_MR_PROMISC	1
 #define PACKET_MR_ALLMULTI	2
+#define PACKET_MR_UNICAST	3
 
 #endif

net/packet/af_packet.c

@@ -1570,9 +1570,9 @@ static int packet_dev_mc(struct net_device *dev, struct packet_mclist *i,
 	switch (i->type) {
 	case PACKET_MR_MULTICAST:
 		if (what > 0)
-			dev_mc_add(dev, i->addr, i->alen, 0);
+			return dev_mc_add(dev, i->addr, i->alen, 0);
 		else
-			dev_mc_delete(dev, i->addr, i->alen, 0);
+			return dev_mc_delete(dev, i->addr, i->alen, 0);
 		break;
 	case PACKET_MR_PROMISC:
 		return dev_set_promiscuity(dev, what);
@@ -1580,6 +1580,12 @@ static int packet_dev_mc(struct net_device *dev, struct packet_mclist *i,
 	case PACKET_MR_ALLMULTI:
 		return dev_set_allmulti(dev, what);
 		break;
+	case PACKET_MR_UNICAST:
+		if (what > 0)
+			return dev_unicast_add(dev, i->addr, i->alen);
+		else
+			return dev_unicast_delete(dev, i->addr, i->alen);
+		break;
 	default:;
 	}
 	return 0;