2924: Remove the usage of capabilities, use port 8080 for admin r=nextgens a=nextgens
## What type of PR?
bug-fix
## What does this PR do?
In the real world users can't get them to work... I wonder if they use patched-up kernels or if xattrs are lost somehow... in any case, we can do without capabilities so let's do that.
Ensure that dovecot doesn't attempt to bind a v6 socket if SUBNET6 is not configured
Also, document that systemd-resolve may cause trouble with DNSSEC.
### Related issue(s)
- closes#2906
- closes#2913
## Prerequisites
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.
- [x] In case of feature or enhancement: documentation updated accordingly
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/workflow.html#changelog) entry file.
Co-authored-by: Florent Daigniere <nextgens@freenetproject.org>
