net/ena: support Rx interrupt

net/ena: support Rx interrupt

In order to support asynchronous Rx in the applications, the driver has
to configure the event file descriptors and configure the HW.

This patch configures appropriate data structures for the rte_ethdev
layer, adds .rx_queue_intr_enable and .rx_queue_intr_disable API
handlers, and configures IO queues to work in the interrupt mode, if it
was requested by the application.

Signed-off-by: Michal Krawczyk <mk@semihalf.com>
Reviewed-by: Artur Rojek <ar@semihalf.com>
Reviewed-by: Igor Chauskin <igorch@amazon.com>
Reviewed-by: Shai Brandes <shaibran@amazon.com>
Reviewed-by: Shay Agroskin <shayagr@amazon.com>