Use the old interface when resetting connections

The new one is often null when disconnected, so using the new fails.
In other situations, it's the connections on the old network we want
to reset anyway, so the old code when it would work would also do
the wrong thing (unless new iface == old iface).

bug:9112928
Change-Id: I1fcae89cc3aa9d712e516e7c97cece0b89869bd9