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.