Adjust ENA driver to the new HAL

Adjust ENA driver to the new HAL

* Removed adaptive interrupt moderation (not suported on FreeBSD).
* Use ena_com_free_q_entries instead of ena_com_free_desc.
* Don't use ENA_MEM_FREE outside of the ena_com.
* Don't use barriers before calling doorbells as it's already done in
  the HAL.
* Add function that generates random RSS key, common for all driver's
  interfaces.
* Change admin stats sysctls to U64.

Submitted by:  Michal Krawczyk <mk@semihalf.com>
Obtained from: Semihalf
Sponsored by:  Amazon, Inc.