netns: ipmr: allocate mroute_socket per-namespace.

Preliminary work to make IPv4 multicast routing netns-aware.

Make IPv4 multicast routing mroute_socket per-namespace,
moves it into struct netns_ipv4.

At the moment, mroute_socket is only referenced in init_net.

Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 977f482..4f00722 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -54,5 +54,9 @@
 
 	struct timer_list rt_secret_timer;
 	atomic_t rt_genid;
+
+#ifdef CONFIG_IP_MROUTE
+	struct sock		*mroute_sk;
+#endif
 };
 #endif