net: aquantia: allow rx checksum offload configuration

RX Checksum offloads could not be configured and ignored netdev features
flag for checksumming.

Signed-off-by: Igor Russkikh <igor.russkikh@aquantia.com>
Signed-off-by: Dmitry Bogdanov <dmitry.bogdanov@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>