hw/net: fix mcf_fec driver receiver

hw/net: fix mcf_fec driver receiver

The network mcf_fec driver emulated receive side method is returning a
result of 0 causing the network layer to disable receive for this emulated
device. This results in the guest only ever receiving one packet.

Fix the recieve side processing to return the number of bytes that we
passed back through to the guest.

Signed-off-by: Greg Ungerer <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Message-id: 1435296436[email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>