Description of configuration options for ml2

Configuration option = Default value	Description
mechanism_drivers =	(ListOpt) An ordered list of networking mechanism driver entrypoints to be loaded from the neutron.ml2.mechanism_drivers namespace.
tenant_network_types = local	(ListOpt) Ordered list of network_types to allocate as tenant networks.
type_drivers = local, flat, vlan, gre, vxlan	(ListOpt) List of network type driver entrypoints to be loaded from the neutron.ml2.type_drivers namespace.