[NET] NETNS: Omit net_device->nd_net without CONFIG_NET_NS.

Introduce per-net_device inlines: dev_net(), dev_net_set().
Without CONFIG_NET_NS, no namespace other than &init_net exists.
Let's explicitly define them to help compiler optimizations.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 3be55c8..44cd42f 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -648,7 +648,7 @@
 {
 	struct net_device *dev = ptr;
 
-	if (dev->nd_net != &init_net)
+	if (dev_net(dev) != &init_net)
 		return NOTIFY_DONE;
 
 	if (event == NETDEV_DOWN)
@@ -1405,7 +1405,7 @@
 	int origlen;
 	__u16 len_hops;
 
-	if (dev->nd_net != &init_net)
+	if (dev_net(dev) != &init_net)
 		goto freeit;
 
 	/* Don't mangle buffer if shared */
@@ -1493,7 +1493,7 @@
 static int ltalk_rcv(struct sk_buff *skb, struct net_device *dev,
 		     struct packet_type *pt, struct net_device *orig_dev)
 {
-	if (dev->nd_net != &init_net)
+	if (dev_net(dev) != &init_net)
 		goto freeit;
 
 	/* Expand any short form frames */