Point ovs submodule at platform9/pf9-ovs fork

Repoint the ovs submodule URL from openvswitch/ovs to the Platform9
fork so custom OVS patches can be carried alongside OVN. The submodule
path stays "ovs" because it is hardcoded in the build tooling
(.ci/ci.sh, .ci/linux-build.sh, .ci/ovn-kubernetes/Dockerfile).

The pinned commit is unchanged (d8b97029e); it is reachable from
branch-3.3 on the fork, so submodule init resolves without a bump.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rutvik-pf9

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "ovs"]
 	path = ovs
-	url = https://github.com/openvswitch/ovs.git
+	url = https://github.com/platform9/pf9-ovs.git