move manpage arcstat(1) to arcstat(8).

Adapted from debian upstream [0] commits:
1a3239e6b3b5604bb588c10912f57f32962b38c3
66b7241c965cdce730e76ca59c242fccc267b302

[0] https://salsa.debian.org/zfsonlinux-team/zfs/
Originally-By: Mo Zhou <cdluminate@gmail.com>
Originally-By: Antonio Russo <aerusso@aerusso.net>
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

debian/zfsutils-linux.install

@@ -33,7 +33,7 @@ usr/sbin/arc_summary
 usr/sbin/arcstat
 usr/sbin/dbufstat
 usr/share/bash-completion/completions
-usr/share/man/man1/arcstat.1
+usr/share/man/man8/arcstat.8
 usr/share/man/man1/zhack.1
 usr/share/man/man1/zvol_wait.1
 usr/share/man/man5/