netns: ip6mr: dynamically allocate mfc6_cache_array

Preliminary work to make IPv6 multicast forwarding netns-aware.

Dynamically allocates IPv6 multicast forwarding cache, mfc6_cache_array,
and moves it to struct netns_ipv6. 

At the moment, mfc6_cache_array is only referenced in init_net.

Replace 'ARRAY_SIZE(mfc6_cache_array)' with mfc6_cache_array size: MFC6_LINES.

Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 4ab0cb0..14c1bbe 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -57,6 +57,7 @@
 	struct sock             *igmp_sk;
 #ifdef CONFIG_IPV6_MROUTE
 	struct sock		*mroute6_sk;
+	struct mfc6_cache	**mfc6_cache_array;
 	struct mif_device	*vif6_table;
 	int			maxvif;
 #endif