`dbuf_stats_hash_table_data` can take much longer than it needs to
by repeatedly bzeroing its buffer when in fact the buffer only needs
to be NULL terminated.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#10993
1cb8202b1b