handle short reads as errors and retry. this can happen
on ohci and some ps2 to usb converter. it might'v deen caused
by a recent change on sources handling td overrun differently.
fix error handling. have to check f->ep == nil after recovery
and check packet size. also, use f->ep->dfd instead of ptrfd
and kbdfd as it might be different after recovery. make a
setleds() error non fatal.
boost process priority for keyboard and mouse worker processes.
cleanup: use single write() in putmod(), improve error reporting.
