[NETNS]: Declare init_net even without CONFIG_NET defined.

This seems bogus but there is no other way for now. There are several
placec when networking headers are included even without CONFIG_NET and
the possibility of the similar reports in the nearest future is great.

Signed-off-by: Denis V. Lunev <den@openvz.org>
----
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 6c9a48a..0ab62ed 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -60,11 +60,12 @@ struct net {
 };
 
 
-#ifdef CONFIG_NET
 #include <linux/seq_file_net.h>
 
 /* Init's network namespace */
 extern struct net init_net;
+
+#ifdef CONFIG_NET
 #define INIT_NET_NS(net_ns) .net_ns = &init_net,
 
 extern struct net *copy_net_ns(unsigned long flags, struct net *net_ns);