Limit the number of autoconfigured queues to 8.

This limit was in a previous version of the driver, but it is being re-
added to match the behavior of previous versions of 10. It prevents the
driver from using too many MSI-X vectors on systems with a large number of
logical CPU cores.

Thanks to <jwd@slowblink.com> for bringing up this issue.

Approved by: jfv (mentor)