netdev: introduce dev_get_stats()

In order for the network device ops get_stats call to be immutable, the handling
of the default internal network device stats block has to be changed. Add a new
helper function which replaces the old use of internal_get_stats.

Note: change return code to make it clear that the caller should not
go changing the returned statistics.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/parisc/led.c b/drivers/parisc/led.c
index f9b1266..454b653 100644
--- a/drivers/parisc/led.c
+++ b/drivers/parisc/led.c
@@ -360,13 +360,13 @@
 	read_lock(&dev_base_lock);
 	rcu_read_lock();
 	for_each_netdev(&init_net, dev) {
-	    struct net_device_stats *stats;
+	    const struct net_device_stats *stats;
 	    struct in_device *in_dev = __in_dev_get_rcu(dev);
 	    if (!in_dev || !in_dev->ifa_list)
 		continue;
 	    if (ipv4_is_loopback(in_dev->ifa_list->ifa_local))
 		continue;
-	    stats = dev->get_stats(dev);
+	    stats = dev_get_stats(dev);
 	    rx_total += stats->rx_packets;
 	    tx_total += stats->tx_packets;
 	}