net: dsa: lantiq: Add fast age function

Fast aging per port is not supported directly by the hardware, it is
only possible to configure a global aging time.

Do the fast aging by iterating over the MAC forwarding table and remove
all dynamic entries for a given port.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>