net: ena: improve latency by disabling adaptive interrupt moderation by default

Adaptive interrupt moderation was erroneously enabled by default
in the driver.

In case the device supports adaptive interrupt moderation it will
be automatically used, which may potentially increase latency.

The adaptive moderation can be enabled from ethtool command in
case the feature is supported by the device.

Fixes: 1738cd3e ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Guy Tzalik <gtzalik@amazon.com>
Signed-off-by: Sameeh Jubran <sameehj@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>