be2net: Handle error completion in Lancer

In Lancer if a frame is DMAed partially due to lack of RX buffers,
an error completion is sent with packet size as zero and num_recvd
indicating number of used buffers. These buffers need to be freed
and packet dropped.

Signed-off-by: Padmanabh Ratnakar <padmanabh.ratnakar@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>