net: mvneta: Verify hardware checksum only when offload checksum feature is set

If the checksum offload feature is not set, then there is no point to
check the status of the hardware.

[gregory: extract from a larger patch]
Signed-off-by: Yelena Krivosheev <yelena@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>