zstream currently contains three identical copies of dump_record(),
which appear to all be drawn from libzfs_sendrecv.c. The original
is marked internal.
This PR adds zstream_util.[hc] and puts the shared code there along with
a couple of other items in common.
No functional changes.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Garth Snyder <garth@garthsnyder.com>
Closes#18284
