usbfs: Kill urbs on interface before doing a set_interface

The usb_set_interface documentation says:

 * Also, drivers must not change altsettings while urbs are scheduled for
 * endpoints in that interface; all such urbs must first be completed
 * (perhaps forced by unlinking).

For in kernel drivers we trust the drivers to get this right, but we
cannot trust userspace to get this right, so enforce it by killing any
urbs still pending on the interface.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>