MFV r286682: 5765 add support for estimating send stream size with
lzc_send_space when source is a bookmark

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Steven Hartland <killing@multiplay.co.uk>
Reviewed by: Bayard Bell <buffer.g.overflow@gmail.com>
Approved by: Albert Lee <trisk@nexenta.com>
Author: Max Grossman <max.grossman@delphix.com>

illumos/illumos-gate@643da460c8ca583e39ce053081754e24087f84c8