net: bcmgenet: hook ethtool set/get_wol operations

Now that Wake-on-LAN support mode is fully integrated into the driver,
allow an user to query and configure Wake-on-LAN in the driver.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>