Cilium: overwrite auto-detected MTU of underlying network (#6329)

roles/network_plugin/cilium/defaults/main.yml

@@ -2,6 +2,7 @@
 # Log-level
 cilium_debug: false
 
+cilium_mtu: ""
 cilium_enable_ipv4: true
 cilium_enable_ipv6: false
 

roles/network_plugin/cilium/templates/cilium-ds.yml.j2

@@ -25,6 +25,9 @@ spec:
         - --kvstore=etcd
         - --kvstore-opt=etcd.config=/var/lib/etcd-config/etcd.config
         - --config-dir=/tmp/cilium/config-map
+{% if cilium_mtu != "" %}
+        - --mtu={{ cilium_mtu }}
+{% endif %}
         command:
         - cilium-agent
         env: