MT7530 has a global address age control register, so use it to set
ageing time.

The applied timer is (AGE_CNT + 1) * (AGE_UNIT + 1) seconds
Signed-off-by: NDENG Qingfang <dqfext@gmail.com>
Reviewed-by: NAndrew Lunn <andrew@lunn.ch>
Reviewed-by: NVladimir Oltean <olteanv@gmail.com>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>