net: bcmgenet: add WAKE_FILTER support

This commit enables support for the WAKE_FILTER method of Wake on
LAN for the GENET driver. The method can be enabled by adding 'f'
to the interface 'wol' setting specified by ethtool.

Rx network flow rules can be specified using ethtool. Rules that
define a flow-type with the RX_CLS_FLOW_WAKE action (i.e. -2) can
wake the system from the 'standby' power state when the WAKE_FILTER
WoL method is enabled.

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