It seams that it's not supported to update/add tags with host.mass*

I had a look at CHostGeneral.php and it wasn't noted there.

On the other hand it is possible to mass update host tags in the frontend but it seems https://github.com/zabbix/zabbix/blob/86e41ec878b740666af51e0c04adb5b1541e3a4e/frontends/php/hosts.php that it is not done over api.

As tags are more and more essential (imo) this should be fixed.