updated patch with throttling

[Duncan Sands]

Hi Roman,

> Below is the updated patch which avoids both deadlock and livelock in
> case of repetitive urb submission failures.  It does that by adding two
> timers (for either direction) to make sure the processing is restarted
> after the submission error but with a delay of THROTTLE_MSECS which I
> arbitrarily set to 5.

does this handle stalls?  By the way, IIRC, the previous code was
supposed to work like this: if you had N urbs, and N successive
urb submissions failed, then it was no longer possible to send
packets - the connection needed to be shutdown and reopened in
order to restart.  As a strategy it sucked... but I don't think it
lead to dead- or live-locks.  Did it?

Thanks,

D.