ena: Support LLQ entry size recommendation from device

This commit adds support for receiving LLQ entry size recommendation
from the device. The driver will use the recommended entry size, unless
the user specifically chooses to use regular or large LLQ entry.

Also added enum ena_llq_header_size_policy_t and llq_plociy field in
order to support the new feature.

Approved by: cperciva (mentor)
Sponsored by: Amazon, Inc.

(cherry picked from commit b1c38df05d79c81ee1e9fd0942774820a4ffcb63)