MFC r235222:

MFC r235222:
Import illumos changeset 13686:4bc0783f6064
2703 add mechanism to report ZFS send progress

If the zfs send command is used with the -v flag, the amount of bytes
transmitted is reported in per second updates.

References:
https://www.illumos.org/issues/2703

Obtained from:	illumos (issue #2703)

git-svn-id: svn://svn.freebsd.org/base/stable/8@235952 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f