If enough MSI-X vectors are available, set up multiple tx and rx queues.

If enough MSI-X vectors are available, set up multiple tx and rx queues.
In multi-vector mode, the MSI-X vector number is the same as the irq number
on the nic, so use vector/irq 0 for link interrupts, then assign one to
each pair of rx and tx queues.  We don't configure RSS yet, so packets
will only be received on the first queue, but they can be transmitted on
any queue.

ok dlg@