MFC r305197: MFV r302646:
6980 6902 causes zfs send to break due to 32-bit/64-bit struct mismatch

illumos/illumos-gate@ea4a67f462de0a39a9adea8197bcdef849de5371
https://github.com/illumos/illumos-gate/commit/ea4a67f462de0a39a9adea8197bcdef84
9de5371

https://www.illumos.org/issues/6980

doing zfs send -i snap1 snap2 >testfile results in
internal error: Invalid argument
Abort (core dumped)

Reviewed by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Matthew Ahrens <mahrens@delphix.com>