ena: Support LLQ entry size recommendation from device

To allow ENA driver to configure LLQ size according to device's
default size which is now being published via ENA_ADMIN_GET_FEATURE
command, and updated ena_admin_def.h.

new definitions:
(1) entry_size_recommended field was introduced in the ENA_ADMIN_LLQ

feature struct and is being used to set LLQ size in case user did
not specify otherwise.

(2) llq_feature_version enum was introduced to allow struct changes

within command - see (1)

From now on, when querying ENA_ADMIN_LLQ feature, we use current version
(ENA_ADMIN_LLQ_FEATURE_VERSION_1) instead of hard-coded 0.

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