ovs: Fix OVS path mismatch when building from source with OVN

``compile_ovs`` was called with ``--localstatedir=/var``, causing
all compiled OVS binaries to hardcode ``/var/run/openvswitch`` as
the default runtime directory. However, the ``ovn_agent`` plugin
derives ``OVS_RUNDIR`` from ``OVS_PREFIX`` as
``/usr/local/var/run/openvswitch``, creating a path mismatch that
makes ``ovs-vsctl`` unable to reach the running ``ovsdb-server``.

Additionally, ``start_new_ovs`` was unconditionally starting OVS
during the install phase. When OVN is the backend,
``ovn_agent:_start_ovs`` later starts its own OVS instance with a
separate database, but the orphaned ``ovs-vswitchd`` from
``start_new_ovs`` still holds the kernel datapath, preventing
bridge creation.

Fix both issues:
- Remove the ``--localstatedir=/var`` override so the compiled
  default matches ``OVS_RUNDIR`` (autotools defaults localstatedir
  to ``${prefix}/var``).
- Skip ``start_new_ovs`` when OVN services are enabled, since
  ``_start_ovs`` handles the full OVS lifecycle.
- Fix the hardcoded DB path in ``start_new_ovs`` to match the
  compiled ``--prefix=/usr/local`` sysconfdir.

Closes-Bug: #2158954
Assisted-By: Claude Opus 4.6
Signed-off-by: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Change-Id: I8f3a2c5e7d1b4a9f6e0c3d8b2a5f7e1d4c6b9a0e

lib/neutron_plugins/ovs_base

@@ -68,9 +68,15 @@ function _neutron_ovs_base_install_ubuntu_dkms {
 function _neutron_ovs_base_install_agent_packages {
     if [ "$Q_BUILD_OVS_FROM_GIT" == "True" ]; then
         remove_ovs_packages
-        compile_ovs /usr/local /var
+        compile_ovs /usr/local
         load_conntrack_gre_module
-        start_new_ovs
+        # When OVN is the backend, ovn_agent:_start_ovs handles OVS
+        # lifecycle with its own DB and rundir. Starting OVS here would
+        # leave an orphaned ovs-vswitchd holding the kernel datapath,
+        # preventing the OVN-managed instance from creating bridges.
+        if ! is_service_enabled ovn-controller ovn-northd; then
+            start_new_ovs
+        fi
     else
         # Install deps
         install_package $(get_packages "openvswitch")

lib/neutron_plugins/ovs_source

@@ -128,7 +128,8 @@ function action_openvswitch {
 
 # start_new_ovs() - removes old ovs database, creates a new one and starts ovs
 function start_new_ovs {
-    sudo rm -f /etc/openvswitch/conf.db /etc/openvswitch/.conf.db~lock~
+    # DB path must match the compiled --prefix=/usr/local sysconfdir
+    sudo rm -f /usr/local/etc/openvswitch/conf.db /usr/local/etc/openvswitch/.conf.db~lock~
     sudo /usr/local/share/openvswitch/scripts/ovs-ctl start
 }