http2 directive

to reduce warns in logs

backend/templates/_listen.conf

@@ -5,11 +5,16 @@
   #listen [::]:80;
 {% endif %}
 {% if certificate -%}
-  listen 443 ssl{% if http2_support == 1 or http2_support == true %} http2{% endif %};
+  listen 443 ssl;
 {% if ipv6 -%}
-  listen [::]:443 ssl{% if http2_support == 1 or http2_support == true %} http2{% endif %};
+  listen [::]:443 ssl;
 {% else -%}
   #listen [::]:443;
 {% endif %}
 {% endif %}
   server_name {{ domain_names | join: " " }};
+{% if http2_support == 1 or http2_support == true %}
+  http2 on;
+{% else -%}
+  http2 off;
+{% endif %}