IRoute: remove setEnabled(), isEnabled() and isExpired() methods
IRoute: add sourceType field (was called source in INET 2.0)
IPv4Route: remove unused 'adapter' field
IRoutingTable: remove purgeExpiredRoutes() method
IPv4RoutingTable: remove unused 'adapter' field
IPv6: IPv6Route and IPv6RoutingTable changes

- fix implementation of the IRoute interface
- consistent use of delete.../remove... method names in IPv6RoutingTable
- fix memory leaks (removed routes was never deleted)
- store interface ptr in the route (instead of interface id)