Fix disconnect abort
Detail: For a long while XCHIDriver has produced aborts on disconnect. This means the e.g. Pi4 based machines cannot in practice be used with KVM swiitches. After 3 or 4 switchovers there will be an abort. This has been identified as being a call to xhci_timeout() on a pipe that is no longer there. This is a solution:
Reenable callout_stop() in xhci_abort_transfer(). Abort was seen when xhci_timeout() was fired (inappropriately) after transfer had been aborted.
Admin: