net: ena: Enable DIM by default

Dynamic Interrupt Moderation (DIM) is a technique
designed to balance the need for timely data processing
with the desire to minimize CPU overhead.
Instead of generating an interrupt for every received
packet, the system can dynamically adjust the rate at
which interrupts are generated based on the incoming
traffic patterns.

Enabling DIM by default to improve the user experience.

DIM can be turned on/off through ethtool:
`ethtool -C <interface> adaptive-rx <on/off>`

Signed-off-by: Arthur Kiyanovski <akiyano@amazon.com>
Signed-off-by: Osama Abboud <osamaabb@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>