IPoIB: Turn on interface's carrier after broadcast group is joined

Do netif_carrier_on() right after the IPv4 broadcast multicast group
is joined, rather than waiting for all of the initial set of multicast
group joins to finish.  This allows at least IPv4 traffic to limp
along on broken fabrics where not all multicast groups can be joined.
Signed-off-by: Shirley Ma <xma@us.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -407,6 +407,10 @@ static int ipoib_mcast_join_complete(int status,
 			queue_delayed_work(ipoib_workqueue,
 					   &priv->mcast_task, 0);
 		mutex_unlock(&mcast_mutex);
+
+		if (mcast == priv->broadcast)
+			netif_carrier_on(dev);
+
 		return 0;
 	}
 
@@ -594,7 +598,6 @@ void ipoib_mcast_join_task(struct work_struct *work)
 	ipoib_dbg_mcast(priv, "successfully joined all multicast groups\n");
 
 	clear_bit(IPOIB_MCAST_RUN, &priv->flags);
-	netif_carrier_on(dev);
 }
 
 int ipoib_mcast_start_thread(struct net_device *dev)