bridge: netlink: add fdb flush

Simple attribute that flushes the bridge's fdb.

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 eaeaac1..9ca9bf8 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -244,6 +244,7 @@
 	IFLA_BR_TOPOLOGY_CHANGE_TIMER,
 	IFLA_BR_GC_TIMER,
 	IFLA_BR_GROUP_ADDR,
+	IFLA_BR_FDB_FLUSH,
 	__IFLA_BR_MAX,
 };