salt: Ensure we do not have multi cidr for Control Plane with MetalLB

Today we do not support multiple subnet for Control Plane network when
MetalLB is enabled, so this commit check that it's not the case

See: #3502

CHANGELOG.md

@@ -11,6 +11,13 @@
 - Fix UI issues in multi nodes environment when a node
   is unavailable (PR[#3521](https://github.com/scality/metalk8s/pull/3521))
 
+## Bug fixes
+
+- Manage Control Plane Ingress Virtual IP with MetalLB is not
+  supported when you have multiple subnet in Control Plane
+  network, now it's properly checked
+  (PR [#](https://github.com/scality/metalk8s/pull/))
+
 ## Release 2.10.2
 ### Bug fixes
 - Fix the link to documentation from the UI navigation bar

salt/_pillar/metalk8s.py

@@ -94,13 +94,19 @@ def _load_networks(config_data):
     # MetalLB disabled by default
     networks_data["controlPlane"].setdefault("metalLB", {}).setdefault("enabled", False)
 
-    if networks_data["controlPlane"]["metalLB"]["enabled"] and not networks_data[
-        "controlPlane"
-    ].get("ingress", {}).get("ip"):
-        errors.append(
-            "'ip' for 'ingress' in 'controlPlane' network is mandatory when 'metalLB'"
-            "is enabled"
-        )
+    if networks_data["controlPlane"]["metalLB"]["enabled"]:
+        if not networks_data["controlPlane"].get("ingress", {}).get("ip"):
+            errors.append(
+                "'ip' for 'ingress' in 'controlPlane' network is mandatory when "
+                "'metalLB' is enabled"
+            )
+        if len(networks_data["controlPlane"]["cidr"]) > 1:
+            errors.append(
+                "Control Plane Ingress Virtual IP management with MetalLB is "
+                "currently not supported when you have multiple subnet for "
+                "Control Plane network, see "
+                "https://github.com/scality/metalk8s/issues/3502"
+            )
 
     if errors:
         return __utils__["pillar_utils.errors_to_dict"](errors)