bridge: netlink: export bridge id

Add IFLA_BR_BRIDGE_ID and export br->bridge_id 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 0381437..7484954 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -234,6 +234,7 @@
 	IFLA_BR_VLAN_PROTOCOL,
 	IFLA_BR_GROUP_FWD_MASK,
 	IFLA_BR_ROOT_ID,
+	IFLA_BR_BRIDGE_ID,
 	__IFLA_BR_MAX,
 };