Set feature gates in kube-proxy ConfigMap (#6851)

Command line flags aren't added to kube-proxy which results in missing
feature gates set in this component. Add appropriate setting to
ConfigMap instead.

Signed-off-by: Maciej Wereski <m.wereski@partner.samsung.com>

roles/kubernetes/master/templates/kubeadm-config.v1beta2.yaml.j2

@@ -375,6 +375,12 @@ nodePortAddresses: {{ kube_proxy_nodeport_addresses }}
 oomScoreAdj: {{ kube_proxy_oom_score_adj }}
 portRange: {{ kube_proxy_port_range }}
 udpIdleTimeout: {{ kube_proxy_udp_idle_timeout }}
+{% if kube_feature_gates %}
+featureGates:
+{% for feature in kube_feature_gates %}
+  {{ feature|replace("=", ": ") }}
+{% endfor %}
+{% endif %}
 {# DNS settings for kubelet #}
 {% if enable_nodelocaldns %}
 {% set kubelet_cluster_dns = [nodelocaldns_ip] %}