Detect mismatch in publishing prefix with local connectivity and warn user

[jburkeucla]

The user will get inconsistent application behavior (receive-only, including in chat) if their publishing prefix in ndnrtc doesn't match their local connectivity.

Suggestion:

1. Periodically get local prefix by sending interest: /localhop/nfd/rib/routable-prefixes
   http://named-data.net/doc/NFD/current/misc/local-prefix-discovery.html#local-prefix-discovery

2. Warn user if there is a mismatch, and provide option to replace / update the name.
   (This requires some guessing at what the previous prefix was...)