Always allow abort tasks to be scheduled, even if the device is beeing

Always allow abort tasks to be scheduled, even if the device is beeing
detached, in order to prevent a deadlock situation.

This situation can occur if the thread detaching a device is sleeping,
waiting for all submitted transfers to finish, and the device's pipes
have not yet been aborted.  This can happen when a USB Ethernet device
is being detached while a userland program is doing an ioctl(2).

Abort tasks need to be able to run in such case since timed out transfers
rely on them to be properly completed.

ok deraadt@