helm: enforce routing-mode when {gke,aksbyocni}.enabled is set.

Historically, the Cilium helm chart allowed to override the routing mode
leveraged in combination with {gke,aksbyocni}.enabled. This is no longer
possible since aff16b2 ("Change routing-mode and tunnel interaction.").

According to the Cilium documentation [1,2], this appears to be the
correct behavior, as the routing mode must be respectively set to native
and tunnel in these cases. Hence, let's validate that users didn't
configure a different routing mode, to avoid falling back silently,
which may be confusing.

[1]: https://docs.cilium.io/en/stable/network/concepts/routing/#id6
[2]: https://docs.cilium.io/en/stable/gettingstarted/k8s-install-default/#install-cilium (AKS tab)

Signed-off-by: Marco Iorio <[email protected]>

install/kubernetes/cilium/templates/cilium-configmap.yaml

@@ -448,9 +448,15 @@ data:
   #   - vxlan (default)
   #   - geneve
 {{- if .Values.gke.enabled }}
+  {{- if ne (.Values.routingMode | default "native") "native" }}
+    {{- fail (printf "RoutingMode must be set to native when gke.enabled=true" )}}
+  {{- end }}
   routing-mode: "native"
   enable-endpoint-routes: "true"
 {{- else if .Values.aksbyocni.enabled }}
+  {{- if ne (.Values.routingMode | default "tunnel") "tunnel" }}
+    {{- fail (printf "RoutingMode must be set to tunnel when aksbyocni.enabled=true" )}}
+  {{- end }}
   routing-mode: "tunnel"
   tunnel-protocol: "vxlan"
 {{- else if .Values.routingMode }}