Arguably, we currently only have one instance of NMPlatform,
NMRouteManager, NMDefaultRouteManager -- the one owned by the
NMNetns singleton.

Hence, all these instances we create with "log-with-ptr" set explicitly
to false.

In the future we want to support namespaces, and it will be be common to
have multiple instances. For that we have "log-with-ptr" so we are able
to disambiguiate the logging.

Change the default to TRUE because it makes more sense. It has currently
no effect as the default is never used.