ena: Support max wide LLQ depth from device

[osamaabb_amazon.com]

Summary

In order to support the change in the way drivers get the
maximal depth for wide LLQ,
max_wide_llq_depth was added to struct ena_admin_feature_llq_desc and
will hold the device's exact maximal size as reported by the device,
this way the driver doesn't have to calculate it in a hardcoded manner.

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