xen-netfront: use netif_start_queue() on xennet_open()

xen-netfront never called netif_start_queue() and was was waking the
queue on xennet_open(), triggering the BUG_ON() on __netif_schedule().

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/net/xen-netfront.c

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 902bbe7..c749bdb 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -329,7 +329,7 @@
 	}
 	spin_unlock_bh(&np->rx_lock);
 
-	xennet_maybe_wake_tx(dev);
+	netif_start_queue(dev);
 
 	return 0;
 }