fix for ixgbe to use non-power-of-2 number of rx queues

[Kip Macy]

Unless anyone complains I intend to commit the following change to
HEAD. It makes it possible to use an arbitrary number of rx queues up
to the maximum allowed by hardware. The current driver only allows 1,
2, 4, or 8.

http://www.fsmware.com/ixgbe.diff