nginx uses SSL mode for a listen socket with any option set,
the bug has been introduced in r3765
diff --git a/src/http/ngx_http.c b/src/http/ngx_http.c
index 58fc7af..4ecd50c 100644
--- a/src/http/ngx_http.c
+++ b/src/http/ngx_http.c
@@ -1274,7 +1274,7 @@
         default_server = addr[i].opt.default_server;
 
 #if (NGX_HTTP_SSL)
-        ssl = lsopt->ssl || addr[i].opt.set;
+        ssl = lsopt->ssl || addr[i].opt.ssl;
 #endif
 
         if (lsopt->set) {