usb4bsd - Fix poll/select/kqfilter issues with ums and usb_fifo*() API

usb4bsd - Fix poll/select/kqfilter issues with ums and usb_fifo*() API

* Fix handling of f->flag_isselect.  It was being improperly cleared on
  event notification.  It can only be cleared when the knote is removed.

* Call f->methods->f_start_read() unconditionally in usb_filter_read().
  Conditionalizing on f->queue_data will fail with devices (aka ums) which
  allocate the buffer independantly of starting the interrupt xfer.

* Call usb_fifo_wakeup() in mbuf re-queue cases to handle races when
  the read() code pulls an mbuf off the queue and then puts it back on.

* Fix bugs in UMS - Keep track of whether the interrupt transfer is running
  or not and do not re-submit or re-stop the transfer unconditionally.