Comment 4 for bug 1716964

As the comment says in the vlan if-up script, this setting has nothing to do with vlans and really should go into ifupdown itself; it makes no sense for the setting to only work if the 'vlan' package is installed (and it will work for vlan and non-vlan interfaces as long as 'vlan' is installed).

However, since this is 'how it has always worked' with ifupdown and nobody has complained, and ifupdown is riding into the sunset, it makes no sense to do more than the minimum to fix this. I'll make the tweak to the vlan if-up script and leave it at that.