migrate to "export default"

also, set no-use-before-define in linter

src/network/network-interface.js

@@ -6,12 +6,6 @@ import safe from 'safetydance';
 
 const debug = debugModule('box:network/network-interface');
 
-export {
-    getIPv4,
-    getIPv6,
-    testIPv4Config,
-    testIPv6Config
-};
 
 async function getIPv4(config) {
     assert.strictEqual(typeof config, 'object');
@@ -58,3 +52,10 @@ async function testIPv6Config(config) {
     const [error] = await safe(getIPv6(config));
     return error || null;
 }
+
+export default {
+    getIPv4,
+    getIPv6,
+    testIPv4Config,
+    testIPv6Config
+};