net/ena: prevent double doorbell

net/ena: prevent double doorbell

Add per-tx-ring flag for packets that were pushed to HW but await
doorbell. That is to prevent a situation when a doorbell is sent due to
reaching Tx burst threshold and next send fails (e.g., due to queue
full). In such case we shouldn't send another doorbell because there are
no actual packets waiting for transmission.

Fixes: c7519ea5eb8d ("net/ena: call additional doorbells if needed")
Cc: stable@dpdk.org
Signed-off-by: Igor Chauskin <igorch@amazon.com>
Reviewed-by: Michal Krawczyk <mk@semihalf.com>