rocker: add flow install/refresh time to track refresh learned FDB entries

If there are hits on a learned src-mac/vlan entry in the bridging table,
send refresh events to driver to keep FDB entry alive and reset aging timers.
Refresh events aren't send more frequently that once a second for a given
src_mac/vlan.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>