NFD

In NFD-RIB, publish a routable-prefixes dataset.
Collect routable-prefixes from connected gateway routers to populate this dataset.

This issue includes:

• Declare a configuration option to specify the prefixes announced by this host. The default value is an empty list. On an end host, this option should be empty. On a router, this option should contain the prefixes announced by this router into the global routing system.
• Implement #3143 procedure in NFD-RIB. Collect routable-prefixes dataset from every connected gateway router.
• Compute registerable prefixes, which is the intersection of routable-prefixes collected from connected routers, and the prefixes this host has certificates to register.
• Publish a routable-prefixes StatusDataset under RibMgmt, which contains the union of announced prefixes and registerable prefixes.

NFD Developer Guide should be updated to reflect the change.