ifupdown on GNU/kFreeBSD

[Petr Salinger <Petr.Salinger@seznam.cz>]

> Forcing the upgrade does not seem to break DHCP interfaces.
> However, lo0 no longer works:

IMHO, the best way to solve this is to have os-specific set of
commands, which ifupdown execute.

It would allow us to stop wrapping ifconfig and route
and install them directly.
For previous problems see also #605723.

Petr