neutron-mlnx-agent: pin pyzmq at 21.*

20.* fails to build so let us try version where upstream fixed packaging
issues.

Change-Id: I099b21872a12c2dccaba4065965d9227ee2e87bc
(cherry picked from commit b2d5307)

Author: Marcin Juszkiewicz

docker/neutron/neutron-mlnx-agent/Dockerfile.j2

@@ -17,10 +17,12 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
 {{ macros.install_packages(neutron_mlnx_agent_packages | customizable("packages")) }}
 
 {% set neutron_mlnx_agent_pip_packages = [
-    'networking-mlnx'
+    'networking-mlnx',
 ] %}
 
-RUN {{ macros.install_pip(neutron_mlnx_agent_pip_packages | customizable("pip_packages")) }}
+{# NOTE(hrw): pyzmq 20 fails to build while 19.* and 21.* build fine. #}
+RUN sed -e "s/^pyzmq===20.0.0/pyzmq==21.*/g" -i /requirements/upper-constraints.txt \
+    && {{ macros.install_pip(neutron_mlnx_agent_pip_packages | customizable("pip_packages")) }}
 
 {% block neutron_mlnx_agent_footer %}{% endblock %}
 {% block footer %}{% endblock %}