ena: Handle ENA_CMD_ABORTED case on admin queue interrupt mode

Currently admin_queue->stats.aborted_cmd counter is incremented if an
admin command status is ENA_CMD_ABORTED and only if the admin queue is
in polling mode.
This commit fixes handling the case of incrementing
admin_queue->stats.aborted_cmd if the admin queue is in interrupt
mode as well.
Also added a verification that the command status is a valid
completion status which is currently verified only if the admin queue
is in polling mode.

Approved by: cperciva (mentor)
MFC after: 2 weeks
Sponsored by: Amazon, Inc.