s390/qeth: switch to napi_gro_receive

Add support for GRO (generic receive offload) in the layer 2
part of device driver qeth. This results in a performance
improvement when GRO and RX is turned on.

Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>