RN: Packager URL defaults to port 8081 if no port in bundleURL

Summary:The packager url for the persistent connection relied on a port
in the bundleURL, so we need to insert a sensible default. Otherwise,
issues occur: https://github.com/facebook/react-native/issues/6581

Reviewed By: bestander

Differential Revision: D3113034

fb-gh-sync-id: 4eac52631ad7abd343b75a4488bb591b5caf2145
fbshipit-source-id: 4eac52631ad7abd343b75a4488bb591b5caf2145

React/Modules/RCTDevMenu.m

@@ -239,6 +239,9 @@ RCT_EXPORT_MODULE()
 
   NSString *scheme = [_bridge.bundleURL scheme];
   NSNumber *port = [_bridge.bundleURL port];
+  if (!port) {
+    port = @8081; // Packager default port
+  }
   return [NSURL URLWithString:[NSString stringWithFormat:@"%@://%@:%@/message?role=shell", scheme, host, port]];
 }