ovn: use bundled ovs

We are using the latest OVS, however, OVN needs to build using the
OVS submodule since some of the signatures don't work[1].

[1]: https://github.com/ovn-org/ovn/issues/128

Change-Id: I3ad7e5e80f1141c3d94f7ce7c8b8f8fdb9fb7c3c
1 file changed