Some clouds, like OSIC and v1 of DreamCompute, have a split stack
network. This means that a single Neutron Network has both an IPv4 and
an IPv6 subnet, but that the IPv4 subnet is a private/RFC-1918 and the
IPv6 subnet is a Global network. As any inferrance information is
attached to the Network, it's impossible to properly categorize IP
addresses that are on the Server in such a scenario.
Add support for ipv4 and ipv6 versions of the current routes_externally
config value, with each of them defaulting to the value of the
un-specialized routes_externally.
Change-Id: I1e87a1423d20eac31175f44f5f7b38dfcf3a11cb
9d757b3a9a