atl1c: switch to napi_gro_receive

Changing to napi_gro_receive() improves efficiency significantly. Tested
on Intel Core2-based motherboards and iperf3.

Signed-off-by: Sieng Piaw Liew <liew.s.piaw@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>