Fixed warning.
Fixed potential RX queue mishandling.

When more than half of the RX queue was used, the old code stopped processing packets
to avoid monopolizing CPU time. In this situation we re-raise the IRQ again to come
back later.
Increase queue lengths to realistic sizes.
Jacek says this devices works fine. :)
Warn only once on receiver overrun. Since the queue is now pretty long, this should be very rare.