NFD

Steps to reproduce:

1. On an Android phone, run a ndn-js consumer application in Chrome. This application shall send one or more Interests, wait until all Interests being satisfied or timed out, and keep the WebSocket connection open.
   note: You cannot reproduce this bug if router attempts to send something to the phone after step 3.
2. Look at router's nfd-status output or status webpage, remember FaceId for the WebSocket connection from the phone.
   note: The phone's public IP address, combined with a non-busy router, would be helpful to identify the correct face.
3. Turn off WiFi on the phone.
   note: It's important to turn off WiFi before closing webpage.
4. Close webpage in Chrome.
   note: After this step, you may turn on WiFi and continue using the phone. The phone is no longer needed.
5. Wait 8 hours.
6. Look at nfd-status output or status webpage.

Expected: the WebSocket face is gone.

Actual: the WebSocket face persists.

Suggested fix:

• WebSocket face should be marked on-demand.
• When underlying TCP connection disconnects due to lack of keep alive, the WebSocket face should be closed.