Clone of https://bugs.launchpad.net/neutron/+bug/2131664

Description copied from LP:
 

When the baremetal ML2 mechanism driver is configured alongside other ML2 drivers, and VLAN transparent networks are required, the configuration fails because Neutron validates VLAN transparency support across all mechanism drivers.

The baremetal ML2 driver currently reports support for both flat and vlan network types (hardcoded in get_allowed_network_types()), but does not support VLAN transparency. This causes Neutron to raise an error when attempting to create VLAN transparent networks, even when the baremetal driver is only intended to handle flat networks.

If Neutron would only consider ML2 drivers supporting the network type when checking if VLAN transparency is supported it might be possible to relax the constraints - for example allow VLAN Transparent VXLAN/Geneve networks while using ML2 baremetal for flat and/or VLAN networks.