parse: fix renderer validation for nm-devices

When we process a nm-device we check to see if the renderer is
NetworkManager. If it's not set to NetworkManager we log a warning
message and change the backend.

This verification can be only done after the netdef is processed. Move
the verification so it happens after the call to process_mapping().

Fixes LP: #2091755

src/parse.c

@@ -3376,11 +3376,6 @@ handle_network_type(NetplanParser* npp, yaml_node_t* node, const char* key_prefi
             case NETPLAN_DEF_TYPE_NM:
                 g_debug("netplan: %s: handling NetworkManager passthrough device, settings are not fully supported.", npp->current.netdef->id);
                 handlers = ethernet_def_handlers;
-                if (npp->current.netdef->backend != NETPLAN_BACKEND_NM) {
-                    g_debug("nm-device: %s: the renderer for nm-devices must be NetworkManager, it will be used instead of the defined one.",
-                              npp->current.netdef->id);
-                    npp->current.netdef->backend = NETPLAN_BACKEND_NM;
-                }
                 break;
             default: g_assert_not_reached(); // LCOV_EXCL_LINE
         }
@@ -3409,6 +3404,12 @@ handle_network_type(NetplanParser* npp, yaml_node_t* node, const char* key_prefi
             }
         }
 
+        if (npp->current.netdef->type == NETPLAN_DEF_TYPE_NM && npp->current.netdef->backend != NETPLAN_BACKEND_NM) {
+            g_debug("nm-device: %s: the renderer for nm-devices must be NetworkManager, it will be used instead of the defined one.",
+                    npp->current.netdef->id);
+            npp->current.netdef->backend = NETPLAN_BACKEND_NM;
+        }
+
         /* Postprocessing */
         /* Implicit VXLAN settings, which can be deduced from parsed data. */
         if (npp->current.netdef->type == NETPLAN_DEF_TYPE_TUNNEL &&