BSD: When we get RTM_NEWADDR the interface must have IFF_UP.

BSD: When we get RTM_NEWADDR the interface must have IFF_UP.

This is apparently historic behaviour.
It's not always mirrored in RTM_IFINFO either so we need to
replicate the behaviour if we had got it earlier.

This fixes dhcpcd requiring at least something to set the interface
up before starting on OpenBSD.
Other BSD are less impacted because it's a lot harder to get into
this state as we have more control over setting the IPv6 LL address.