Minor updates:

  - Reduce memory utilization in two ways:

     * Dynamically, by pre-allocating all the usb_request objects
       that will be used; if the pre-allocated ones are in use,
       then tx will throttle down.  This behaves better under
       heavy load.

     * Statically, by pre-allocating fewer such requests in the
       typical "no DMA queueing" case ... the best we can do is
       make sure that when the next completion IRQ fires, the
       controller already has a transfer ready.  Having queues
       deeper than two elements only helps if the CPU doesn't
       need to start each transfer by hand (as with net2280).

  - Diagnostics look more like other network driver diagnostics;
    they use the network interface name.