[NETNS][IPV6]: Make the ipv6 sysctl to be a netns subsystem.

The initialization of the sysctl for the ipv6 protocol is changed to a
network namespace subsystem. That means when a new network namespace
is created the initialization function for the sysctl will be called.

That do not change the behavior of the sysctl in case of the kernel
with the network namespace disabled.
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/sysctl_net_ipv6.c

@@ -91,10 +91,10 @@ EXPORT_SYMBOL_GPL(net_ipv6_ctl_path);
 
 static struct ctl_table_header *ipv6_sysctl_header;
 
-int ipv6_sysctl_register(void)
+static int ipv6_sysctl_net_init(struct net *net)
 {
-	ipv6_sysctl_header = register_sysctl_paths(net_ipv6_ctl_path,
-						   ipv6_table);
+	ipv6_sysctl_header = register_net_sysctl_table(net, net_ipv6_ctl_path,
+						       ipv6_table);
 	if (!ipv6_sysctl_header)
 		return -ENOMEM;
 
@@ -102,7 +102,22 @@ int ipv6_sysctl_register(void)
 
 }
 
+static void ipv6_sysctl_net_exit(struct net *net)
+{
+	unregister_net_sysctl_table(ipv6_sysctl_header);
+}
+
+static struct pernet_operations ipv6_sysctl_net_ops = {
+	.init = ipv6_sysctl_net_init,
+	.exit = ipv6_sysctl_net_exit,
+};
+
+int ipv6_sysctl_register(void)
+{
+	return register_pernet_subsys(&ipv6_sysctl_net_ops);
+}
+
 void ipv6_sysctl_unregister(void)
 {
-	unregister_sysctl_table(ipv6_sysctl_header);
+	unregister_pernet_subsys(&ipv6_sysctl_net_ops);
 }