o Code simplification and refactoring:
    - Move the hacky fallback code out of get_interface_address6() 
      into separate function and get it covered with unit-tests. Resolves
      ticket 14710.

  o Minor bugfixes:
    - When attempting to use fallback technique for network interface
      lookup, disregard loopback and multicast addresses since they are
      unsuitable for public communications.