ena: Add differentiation for missing TX completions reset

This commit adds differentiation for a reset caused by missing tx
completions, by verifying if the driver didn't receive tx
completions caused by missing interrupts.
The cleanup_running field was added to ena_ring because
cleanup_task.ta_pending is zeroed before ena_cleanup() runs.

Also ena_increment_reset_counter() API was added in order to support
only incrementing the reset counter.

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