Install correct version of networking-mlnx for openstack release

Updated neutron_mlnx_agent_pip_packages_override to use the stackhpc
branch based on openstack_release.

Author: jovial

etc/kayobe/kolla.yml

@@ -231,7 +231,7 @@ kolla_build_customizations_common:
   nova_compute_packages_append:
     - python3-libvirt
   neutron_mlnx_agent_pip_packages_override:
-    - networking-mlnx@git+https://opendev.org/x/networking-mlnx@master
+    - networking-mlnx@git+https://opendev.org/x/networking-mlnx@stable/{{ openstack_release }}
 
 #stackhpc_kolla_build_customizations: