[NET]: Make /proc/net per network namespace

This patch makes /proc/net per network namespace.  It modifies the global
variables proc_net and proc_net_stat to be per network namespace.
The proc_net file helpers are modified to take a network namespace argument,
and all of their callers are fixed to pass &init_net for that argument.
This ensures that all of the /proc/net files are only visible and
usable in the initial network namespace until the code behind them
has been updated to be handle multiple network namespaces.

Making /proc/net per namespace is necessary as at least some files
in /proc/net depend upon the set of network devices which is per
network namespace, and even more files in /proc/net have contents
that are relevant to a single network namespace.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 381a77c..a523fa4 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -19,6 +19,7 @@
 #include <linux/inetdevice.h>
 #include <linux/proc_fs.h>
 #include <linux/mutex.h>
+#include <net/net_namespace.h>
 #include <net/sock.h>
 
 #include "nf_internals.h"
@@ -293,7 +294,7 @@
 	}
 
 #ifdef CONFIG_PROC_FS
-	proc_net_netfilter = proc_mkdir("netfilter", proc_net);
+	proc_net_netfilter = proc_mkdir("netfilter", init_net.proc_net);
 	if (!proc_net_netfilter)
 		panic("cannot create netfilter proc entry");
 #endif