[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/ipv4/raw.c b/net/ipv4/raw.c
index 3f68a93..8756d50 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -168,7 +168,7 @@
 	if (hlist_empty(head))
 		goto out;
 
-	net = skb->dev->nd_net;
+	net = dev_net(skb->dev);
 	sk = __raw_v4_lookup(net, __sk_head(head), iph->protocol,
 			     iph->saddr, iph->daddr,
 			     skb->dev->ifindex);
@@ -276,7 +276,7 @@
 	raw_sk = sk_head(&raw_v4_hashinfo.ht[hash]);
 	if (raw_sk != NULL) {
 		iph = (struct iphdr *)skb->data;
-		net = skb->dev->nd_net;
+		net = dev_net(skb->dev);
 
 		while ((raw_sk = __raw_v4_lookup(net, raw_sk, protocol,
 						iph->daddr, iph->saddr,