Override address in listen instead of listenPromise (#1102)

Fixes: #1099

fastify.js

@@ -308,11 +308,6 @@ function build (options) {
   }
 
   function listenPromise (port, address, backlog) {
-    // This will listen to what localhost is.
-    // It can be 127.0.0.1 or ::1, depending on the operating system.
-    // Fixes https://github.com/fastify/fastify/issues/1022.
-    address = address || 'localhost'
-
     if (listening) {
       return Promise.reject(new Error('Fastify is already listening'))
     }
@@ -348,7 +343,11 @@ function build (options) {
       cb = address
       address = undefined
     }
-    address = address || '127.0.0.1'
+
+    // This will listen to what localhost is.
+    // It can be 127.0.0.1 or ::1, depending on the operating system.
+    // Fixes https://github.com/fastify/fastify/issues/1022.
+    address = address || 'localhost'
 
     /* Deal with listen (port, address, cb) */
     if (typeof backlog === 'function') {