This patch resolves a FIXME, which happens to make many of
the VIA problems act significantly less severe.  The change
defers unlinking any QH that just became idle, since it's not
unlikely it'll be used again before many milliseconds pass.

It reduces the number of unlink interrupts (IAA), and means
fewer re-activation issues.  Like: newly queued TDs being
all or partially processed before the QH gets de-activated.
The VIA hardware seems to have some problems in those cases.
(Which are extremely common on 2.4 kernels, and less so on
2.5 because usb-storage streams data much better now.)

It also starts tracking the "lost IAA" errors that I see on
at least one VT8235 motherboard.  It shows in the "registers"
sysfs file.  It'd be good to know if it's just my hardware
that has this problem, or if other folk also see it.