tun: keep link (carrier) state up to date

Currently, only ethtool can get accurate link state of a tap device.
With this patch, IFF_RUNNING and IF_OPER_UP/DOWN are kept up to date as
well.
Signed-off-by: NNolan Leake <nolan@cumulusnetworks.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -149,6 +149,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
 	tfile->tun = tun;
 	tun->tfile = tfile;
 	tun->socket.file = file;
+	netif_carrier_on(tun->dev);
 	dev_hold(tun->dev);
 	sock_hold(tun->socket.sk);
 	atomic_inc(&tfile->count);
@@ -162,6 +163,7 @@ static void __tun_detach(struct tun_struct *tun)
 {
 	/* Detach from net device */
 	netif_tx_lock_bh(tun->dev);
+	netif_carrier_off(tun->dev);
 	tun->tfile = NULL;
 	tun->socket.file = NULL;
 	netif_tx_unlock_bh(tun->dev);
@@ -1574,12 +1576,6 @@ static void tun_set_msglevel(struct net_device *dev, u32 value)
 #endif
 }
 
-static u32 tun_get_link(struct net_device *dev)
-{
-	struct tun_struct *tun = netdev_priv(dev);
-	return !!tun->tfile;
-}
-
 static u32 tun_get_rx_csum(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
@@ -1601,7 +1597,7 @@ static const struct ethtool_ops tun_ethtool_ops = {
 	.get_drvinfo	= tun_get_drvinfo,
 	.get_msglevel	= tun_get_msglevel,
 	.set_msglevel	= tun_set_msglevel,
-	.get_link	= tun_get_link,
+	.get_link	= ethtool_op_get_link,
 	.get_rx_csum	= tun_get_rx_csum,
 	.set_rx_csum	= tun_set_rx_csum
 };