Add config options <compat_ifupdown2_bridge_ports_inherit_vlans>.
In ifupdown2 <bridge-vids> as well as the <bridge-pvid> set on a bridge
interface will be inherited by all member ports if not set explicitly.
When set to 1 ifupdown-ng behaves the same way and will internally copy
both options from the bridge member ports if they are not set on the
member port. Valid values are 0 and 1, the default is 1.
Signed-off-by: Maximilian Wilhelm <max@sdn.clinic>
