Merge #3614

3614: Fix http2 (backport #3613) r=mergify[bot] a=mergify[bot]

## What type of PR?

bug-fix

## What does this PR do?

Fix http2; it does not require IPv6 nor certificates

### Related issue(s)

## 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.

- [ ] 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.
<hr>This is an automatic backport of pull request #3613 done by [Mergify](https://mergify.com).

Co-authored-by: Florent Daigniere <nextgens@freenetproject.org>

core/nginx/conf/nginx.conf

@@ -98,6 +98,7 @@ http {
       set $webdav {{ WEBDAV_ADDRESS }}:5232;
       {% endif %}
       client_max_body_size {{ MESSAGE_SIZE_LIMIT|int + 8388608 }};
+      http2 on;
 
       # Listen on HTTP only in kubernetes or behind reverse proxy
       {% if TLS_FLAVOR in [ 'mail-letsencrypt', 'notls', 'mail' ] %}
@@ -112,7 +113,6 @@ http {
       listen 443 ssl{% if PROXY_PROTOCOL_443 %} proxy_protocol{% endif %};
 {% if SUBNET6 %}
       listen [::]:443 ssl{% if PROXY_PROTOCOL_443 %} proxy_protocol{% endif %};
-      http2 on;
 {% endif %}
 
       include /etc/nginx/tls.conf;

towncrier/newsfragments/3613.bugfix

@@ -0,0 +1 @@
+HTTP/2 does not require ipv6; in fact it does not require SSL certs either