MFC r241009
  Ensure that all cases that enqueue a netgraph item for delivery by a
  ngthread properly set the item's depth to 1.  In particular, prior to this
  change if ng_snd_item failed to acquire a lock on a node, the item's depth
  would not be set at all.  This fix ensures that the error code from rcvmsg/
  rcvdata is properly passed back to the apply callback.  For example, this
  fixes a bug where an error from rcvmsg/rcvdata would not previously
  propagate back to a libnetgraph consumer when the message was queued.

  Reviewed by:  mav
  MFC after:    1 month
  Sponsored by: Sandvine Incorporated