ifupdown.sh : add ifupdown2 workaround

ifupdown.sh : add ifupdown2 workaround

with ifupdown2, we can't call ifup for each ovs_ports in OvsBridge.
But as we define also ovs_bridge for each interface, we can simply add
the bridge here, to be sure that it's exist before adding the interface.

for config, we simply need to replace allow-..., with auto.
I have keeped ovs_ports to avoid config change, but it's not used.

old config
----------
auto vmbr100
iface vmbr100 inet manual
        ovs_type OVSBridge
        ovs_ports bond0 ovsinternalport

allow-vmbr100 ovsinternalport
iface ovsinternalport inet static
        address  172.16.0.10
        netmask  255.255.255.0
        ovs_type OVSIntPort
        ovs_bridge vmbr100
        ovs_options tag=30

allow-vmbr100 bond0
iface bond0 inet manual
        ovs_bonds eno3 eno4
        ovs_type OVSBond
        ovs_bridge vmbr100
        ovs_options bond_mode=balance-slb lacp=active

new config
----------
auto vmbr100
iface vmbr100 inet manual
        ovs_type OVSBridge
        ovs_ports bond0 ovsinternalport

auto ovsinternalport
iface ovsinternalport inet static
        address  172.16.0.10
        netmask  255.255.255.0
        ovs_type OVSIntPort
        ovs_bridge vmbr100
        ovs_options tag=30

auto bond0
iface bond0 inet manual
        ovs_bonds eno3 eno4
        ovs_type OVSBond
        ovs_bridge vmbr100
        ovs_options bond_mode=balance-slb lacp=active