netns: ipmr: dynamically allocate mfc_cache_array

Preliminary work to make IPv4 multicast routing netns-aware.

Dynamically allocate IPv4 multicast forwarding cache, mfc_cache_array,
and move it to struct netns_ipv4.

At the moment, mfc_cache_array 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 edbcccb..0b4285a 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -57,6 +57,7 @@
 
 #ifdef CONFIG_IP_MROUTE
 	struct sock		*mroute_sk;
+	struct mfc_cache	**mfc_cache_array;
 	struct vif_device	*vif_table;
 	int			maxvif;
 #endif