bridge: netlink: allow to flush port's fdb

Add IFLA_BRPORT_FLUSH to allow flushing port's fdb similar to sysfs's
flush.
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/if_link.h

@@ -303,6 +303,7 @@ enum {
 	IFLA_BRPORT_MESSAGE_AGE_TIMER,
 	IFLA_BRPORT_FORWARD_DELAY_TIMER,
 	IFLA_BRPORT_HOLD_TIMER,
+	IFLA_BRPORT_FLUSH,
 	__IFLA_BRPORT_MAX
 };
 #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)

net/bridge/br_netlink.c

@@ -631,6 +631,9 @@ static int br_setport(struct net_bridge_port *p, struct nlattr *tb[])
 			return err;
 	}
 
+	if (tb[IFLA_BRPORT_FLUSH])
+		br_fdb_delete_by_port(p->br, p, 0, 0);
+
 	br_port_flags_change(p, old_flags ^ p->flags);
 	return 0;
 }