Set the browser action icon to off when webrtc is disabled

This is now necessary since the webextension changed to default to on.

Follow up to 095f4a0

From trac 31067

proxy/init-webext.js

@@ -36,6 +36,7 @@ var debug, snowflake, config, broker, ui, log, dbg, init, update, silenceNotific
         missingFeature: true
       });
     });
+    chrome.browserAction.setIcon({ path: { 32: "icons/status-off.png" } });
     return;
   }