[RN] Fix loading config.js from URLs with a non-standard port

`host` contains the hostname:port portion, whereas `hostname` is just the
hostname, not including the port.

react/features/app/functions.native.js

     let room;
 
     if (url) {
-        domain = url.hostname;
+        domain = url.host;
 
         // The room (name) is the last component of pathname.
         room = url.pathname;