rocker: handle setting bridge ageing_time

The FDB cleanup timer will get rescheduled to re-evaluate FDB entries
based on new ageing_time.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>