- added ipv6 listen to ispconfig vhost files on nginx (Fixes #3665)

install/tpl/nginx_apps.vhost.master

 server {
-        listen {apps_vhost_ip}{apps_vhost_port};
+        listen {apps_vhost_ip};
+        listen [::]:{apps_vhost_port};
         ssl {ssl_on};
         {ssl_comment}ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
         {ssl_comment}ssl_certificate /usr/local/ispconfig/interface/ssl/ispserver.crt;

install/tpl/nginx_ispconfig.vhost.master

 server {
         listen {vhost_port};
+        listen [::]:{vhost_port}
 		ssl {ssl_on};
 		{ssl_comment}ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
         {ssl_comment}ssl_certificate /usr/local/ispconfig/interface/ssl/ispserver.crt;