RouteInfo changes.

- Add the interface name.
- Fix a bug where a default route would match an address of
  another protocol (e.g., 0.0.0.0/0 would match 2001::).
- Tweak the hashCode method.
- Write a unit test.

Change-Id: Ida8266de440a9b1d9eaa132f182b9f1ce8978c44