Fix some typescript errors in //aos/network/www/...

The typescript compiler upgrade revealed these.

Change-Id: I882e6a93fe69cd45255ae7885b57467ac6cc7498
diff --git a/aos/network/www/config_handler.ts b/aos/network/www/config_handler.ts
index c554647..8670c0a 100644
--- a/aos/network/www/config_handler.ts
+++ b/aos/network/www/config_handler.ts
@@ -33,7 +33,7 @@
       this.tree_div.appendChild(channel_div);
 
       const input_el = document.createElement('input');
-      input_el.setAttribute('data-index', i);
+      input_el.setAttribute('data-index', i.toString());
       input_el.setAttribute('type', 'checkbox');
       input_el.addEventListener('click', () => this.handleChange());
       channel_div.appendChild(input_el);
@@ -62,7 +62,7 @@
         continue;
       }
       const index = toggle.getAttribute('data-index');
-      const channel = this.config.channels(index);
+      const channel = this.config.channels(Number(index));
       const namefb = builder.createString(channel.name());
       const typefb = builder.createString(channel.type());
       Channel.startChannel(builder);