HAProxy guide update (#12279)

HAproxy reverse proxy guide update to stop sending IPv4-mapped address to HS.

changelog.d/12279.doc

+HAProxy reverse proxy guide update to stop sending IPv4-mapped address to homeserver. Contributed by @villepeh.

docs/reverse_proxy.md

@@ -182,7 +182,7 @@ matrix.example.com {
 
 ```
 frontend https
-  bind :::443 v4v6 ssl crt /etc/ssl/haproxy/ strict-sni alpn h2,http/1.1
+  bind *:443,[::]:443 ssl crt /etc/ssl/haproxy/ strict-sni alpn h2,http/1.1
   http-request set-header X-Forwarded-Proto https if { ssl_fc }
   http-request set-header X-Forwarded-Proto http if !{ ssl_fc }
   http-request set-header X-Forwarded-For %[src]
@@ -195,7 +195,7 @@ frontend https
   use_backend matrix if matrix-host matrix-path
 
 frontend matrix-federation
-  bind :::8448 v4v6 ssl crt /etc/ssl/haproxy/synapse.pem alpn h2,http/1.1
+  bind *:8448,[::]:8448 ssl crt /etc/ssl/haproxy/synapse.pem alpn h2,http/1.1
   http-request set-header X-Forwarded-Proto https if { ssl_fc }
   http-request set-header X-Forwarded-Proto http if !{ ssl_fc }
   http-request set-header X-Forwarded-For %[src]