ipmr/ip6mr: advertise mfc stats via rtnetlink

These statistics can be checked only via /proc/net/ip_mr_cache or
SIOCGETSGCNT[_IN6] and thus only for the table RT_TABLE_DEFAULT.
Advertising them via rtnetlink allows to get statistics for all cache entries,
whatever the table is.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 3dee071..80abe27 100644
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h
@@ -288,6 +288,7 @@
 	RTA_MP_ALGO, /* no longer used */
 	RTA_TABLE,
 	RTA_MARK,
+	RTA_MFC_STATS,
 	__RTA_MAX
 };
 
@@ -408,6 +409,12 @@
 	} u;
 };
 
+struct rta_mfc_stats {
+	__u64	mfcs_packets;
+	__u64	mfcs_bytes;
+	__u64	mfcs_wrong_if;
+};
+
 /****
  *		General form of address family dependent message.
  ****/