ipv4: add mc_count to in_device.

This patch add mc_count to struct in_device and updates
increment/decrement/initilaize of this field in IPv4 and in IPv6.

- Also printing the vfs /proc entry (/proc/net/igmp) is adjusted to
use the new mc_count.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h
index c6f51ad..06fcdb4 100644
--- a/include/linux/inetdevice.h
+++ b/include/linux/inetdevice.h
@@ -25,6 +25,7 @@
 	struct in_ifaddr	*ifa_list;	/* IP ifaddr chain		*/
 	rwlock_t		mc_list_lock;
 	struct ip_mc_list	*mc_list;	/* IP multicast filter chain    */
+	int			mc_count;	          /* Number of installed mcasts	*/
 	spinlock_t		mc_tomb_lock;
 	struct ip_mc_list	*mc_tomb;
 	unsigned long		mr_v1_seen;