[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/arp.c b/net/ipv4/arp.c
index 832473e..3ce2e13 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -242,7 +242,7 @@
 		return -EINVAL;
 	}
 
-	neigh->type = inet_addr_type(dev->nd_net, addr);
+	neigh->type = inet_addr_type(dev_net(dev), addr);
 
 	parms = in_dev->arp_parms;
 	__neigh_parms_put(neigh->parms);
@@ -341,14 +341,14 @@
 	switch (IN_DEV_ARP_ANNOUNCE(in_dev)) {
 	default:
 	case 0:		/* By default announce any local IP */
-		if (skb && inet_addr_type(dev->nd_net, ip_hdr(skb)->saddr) == RTN_LOCAL)
+		if (skb && inet_addr_type(dev_net(dev), ip_hdr(skb)->saddr) == RTN_LOCAL)
 			saddr = ip_hdr(skb)->saddr;
 		break;
 	case 1:		/* Restrict announcements of saddr in same subnet */
 		if (!skb)
 			break;
 		saddr = ip_hdr(skb)->saddr;
-		if (inet_addr_type(dev->nd_net, saddr) == RTN_LOCAL) {
+		if (inet_addr_type(dev_net(dev), saddr) == RTN_LOCAL) {
 			/* saddr should be known to target */
 			if (inet_addr_onlink(in_dev, target, saddr))
 				break;
@@ -424,7 +424,7 @@
 	int flag = 0;
 	/*unsigned long now; */
 
-	if (ip_route_output_key(dev->nd_net, &rt, &fl) < 0)
+	if (ip_route_output_key(dev_net(dev), &rt, &fl) < 0)
 		return 1;
 	if (rt->u.dst.dev != dev) {
 		NET_INC_STATS_BH(LINUX_MIB_ARPFILTER);
@@ -477,7 +477,7 @@
 
 	paddr = skb->rtable->rt_gateway;
 
-	if (arp_set_predefined(inet_addr_type(dev->nd_net, paddr), haddr, paddr, dev))
+	if (arp_set_predefined(inet_addr_type(dev_net(dev), paddr), haddr, paddr, dev))
 		return 0;
 
 	n = __neigh_lookup(&arp_tbl, &paddr, dev, 1);
@@ -709,7 +709,7 @@
 	u16 dev_type = dev->type;
 	int addr_type;
 	struct neighbour *n;
-	struct net *net = dev->nd_net;
+	struct net *net = dev_net(dev);
 
 	/* arp_rcv below verifies the ARP header and verifies the device
 	 * is ARP'able.
@@ -858,7 +858,7 @@
 
 	n = __neigh_lookup(&arp_tbl, &sip, dev, 0);
 
-	if (IPV4_DEVCONF_ALL(dev->nd_net, ARP_ACCEPT)) {
+	if (IPV4_DEVCONF_ALL(dev_net(dev), ARP_ACCEPT)) {
 		/* Unsolicited ARP is not accepted by default.
 		   It is possible, that this option should be enabled for some
 		   devices (strip is candidate)