Use setproctitle to report progress of zfs send

This allows parsing of zfs send progress by checking the process
title.
Doing so requires some changes to the send code in libzfs_sendrecv.c;
primarily these changes move some of the accounting around, to allow
for the code to be verbose as normal, or set the process title. Unlike
BSD, setproctitle() isn't standard in Linux; thus, borrowed it from
libbsd with slight modifications.

Authored-by: Sean Eric Fagan <sef@FreeBSD.org>
Co-authored-by: Ryan Moeller <ryan@iXsystems.com>
Co-authored-by: Ameer Hamza <ahamza@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>
Closes #14376