[IPV4]: Move the devinet pointers on the struct net

This is the core.

Add all and default pointers on the netns_ipv4 and register
a new pernet subsys to initialize them.

Also add the ctl_table_header to register the
net.ipv4.ip_forward ctl.

I don't allocate additional memory for init_net, but use
global devinets.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netns/ipv4.h

@@ -4,6 +4,12 @@
 
 #ifndef __NETNS_IPV4_H__
 #define __NETNS_IPV4_H__
+struct ctl_table_header;
+struct ipv4_devconf;
+
 struct netns_ipv4 {
+	struct ctl_table_header	*forw_hdr;
+	struct ipv4_devconf	*devconf_all;
+	struct ipv4_devconf	*devconf_dflt;
 };
 #endif