[NETNS][FRAGS]: Make the net.ipv4.ipfrag_timeout work in namespaces.

Move it to the netns_frags, adjust the usage and
make the appropriate ctl table writable.

Now fragment, that live in different namespaces can
live for different times.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index 6edce7b..f56e296 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -4,6 +4,9 @@
 struct netns_frags {
 	int			nqueues;
 	atomic_t		mem;
+
+	/* sysctls */
+	int			timeout;
 };
 
 struct inet_frag_queue {
@@ -29,7 +32,6 @@
 struct inet_frags_ctl {
 	int high_thresh;
 	int low_thresh;
-	int timeout;
 	int secret_interval;
 };