Define a separate dir for OVS DPDK vhostuser sockets

Currently when OVS-DPDK is enabled, instances fail to spawn
due to permissions mismatch, see nova bug for details:
https://bugs.launchpad.net/nova/+bug/1670950

This patch defines the path so the dir could be created by the nova
formula [1] with needed permissions, and also used by linux.network [2]
and neutron formulas for proper configuration.

[1] https://gerrit.mcp.mirantis.net/#/c/11213
[2] https://gerrit.mcp.mirantis.net/#/c/10763
[3] https://gerrit.mcp.mirantis.net/#/c/10764/

Related-PROD: PROD-14413

Change-Id: Ibacffe8f31432dc24fd9fd81b159faadcddd062a
diff --git a/neutron/compute/nfv/dpdk.yml b/neutron/compute/nfv/dpdk.yml
index 3f05d53..c8872c7 100644
--- a/neutron/compute/nfv/dpdk.yml
+++ b/neutron/compute/nfv/dpdk.yml
@@ -10,6 +10,9 @@
         dpdk_socket_mem: "${_param:compute_ovs_dpdk_socket_mem}"
         dpdk_lcore_mask: "${_param:compute_ovs_dpdk_lcore_mask}"
         memory_channels: "${_param:compute_ovs_memory_channels}"
+        vhost_socket_dir:
+          name: "openvswitch-vhost"
+          path: "/run/openvswitch-vhost"
   neutron:
     compute:
       dpdk: True