This has minor usbcore cleanups:

DOC:
    - the changes passing a usb_interface to driver probe() and disconnect()
      weren't reflected in their adjacent docs.  likewise they still said
      it was possible to get a null usb_device_id (no more).

    - the (root) hub API restrictions from rmk's ARM patch weren't
      flagged

    - mention the non-dma-coherent cache issue for usb_buffer_alloc()

    - mention disconnect() cleanup issue with usb_{control,bulk}_msg()
      [ you can't cancel those urbs from disconnect() ]

CODE
    - make driver ioctl() use 'usb_interface' too ... this update
      also resolves an old 'one instance per device' bad assumption

    - module locking on driver->ioctl() was goofy, kept BKL way too
      long and didn't try_inc_mod_count() like the rest of usbcore

    - hcd unlink code treated iso inappropriately like interrupt;
      only interrupt still wants that automagic mode

    - move iso init out of ohci into shared submit_urb logic

    - remove interrupt transfer length restriction; hcds that don't
      handle packetization (just like bulk :) should be updated,
      but device drivers won't care for now.