Netvirt does not set br-int to netdev with dpdk

Right now it looks like netvirt is looking for some configuration parameter to decide if a bridge should be created as netdev or system:

https://github.com/opendaylight/netvirt/blob/e477acc8f904f14869777db7a7f4b9cd1b479a4d/vpnservice/elanmanager/elanmanager-impl/src/main/java/org/opendaylight/netvirt/elan/internal/ElanBridgeManager.java#L77

Configuring it this way may work for a user who wants a homogeneous deployment, but it is not valid in other scenarios. For example, in OpenStack when using controller and compute nodes, we want the compute nodes to be in netdev for br-int because they will have vhostuser ports. However, controller nodes will use Neutron DHCP agent, and therefore we want them to use system bridge br-int for regular tap interfaces.

If the configuration option is not provided to netvirt, then netvirt should decide to use netdev or system based on configuration of the OVSDB node. In OVS >= 2.6 this can be determined by checking other_config: dpdk-init="true" in OVS. If DPDK is enabled, then I think it is safe for netvirt to decide to create br-int as netdev type. Otherwise it can create br-int as system.

Note other_config:dpdk-init is not yet part of the OVSDB schema, so it would need to be added. Another option may be to introduce a totally new flag as other_config to each OVSDB node, so that a user may configure (per node) to enable netdev or not.