Small kerneldoc clarifications:

  - more endpoint halt clearing info:
      * some hardware can't do it; which causes problems with drivers
        that want to use multiple interfaces or altsettings.
      * it doesn't affect queuing of data (should help usb-storage
        gadget driver, plus it's more sensible this way);
  - disconnect() callback not guaranteed: some hardware can't tell

Mostly this captures answers to questions I've been asked.