[NETNS]: Fix loopback network namespace initialization.

The core patchset of the network namespace sent by
Eric Biederman does not do dynamic loopback creation.
So there is no call to alloc_netdev_mq which fills the
network namespace field of the netdevice.

This patch assign the loopback to the init network namespace.
Signed-off-by: NDaniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/loopback.c

@@ -225,6 +225,7 @@ struct net_device loopback_dev = {
 				  | NETIF_F_LLTX
 				  | NETIF_F_NETNS_LOCAL,
 	.ethtool_ops		= &loopback_ethtool_ops,
+	.nd_net                 = &init_net,
 };
 
 /* Setup and register the loopback device. */