net: ena: Account for the number of processed bytes in XDP

The size of packets that were forwarded or dropped by XDP wasn't added
to the total processed bytes statistic.

Fixes: 548c4940

 ("net: ena: Implement XDP_TX action")
Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>