net: ena: use CSUM_CHECKED device indication to report skb's checksum status

Set skb->ip_summed to the correct value as reported by the device.
Add counter for the case where rx csum offload is enabled but
device didn't check it.

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>