bridge: netlink: add support for igmp's hash_elasticity

Add IFLA_BR_MCAST_HASH_ELASTICITY to allow setting/getting
br->hash_elasticity via netlink.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index fe5fac5..ca7ca76 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -249,6 +249,7 @@
 	IFLA_BR_MCAST_SNOOPING,
 	IFLA_BR_MCAST_QUERY_USE_IFADDR,
 	IFLA_BR_MCAST_QUERIER,
+	IFLA_BR_MCAST_HASH_ELASTICITY,
 	__IFLA_BR_MAX,
 };