net: bcmgenet: handle UMAC_IRQ_MPD_R interrupt bit

Handle UMAC_IRQ_MPD_R interrupt bit in our workqueue to make sure that
we properly re-configure the GENET adapter from Wake-on-LAN.

bcmgenet_power_up() makes sure that we will not leave the UniMAC
hardware in MagicPacket matching mode, since that would prevent any
other packet from being received.

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