xhci_device_bulk_abort calls xhci_abort_xfer.
When a pipe is aborted the EHCI driver removes any pending transactions and aborts the transfer, the XHCI driver does not but the NetBSD version does abort the transfer from version 1.34.
Added xhci_abort_xfer modified from NetBSD xhci v1.34 and made xhci_device_bulk_abort use it.
This stops SerialUSB locking up the machine when closing a device which is still transferring data when it is closed.
Tested on a raspberry pi.