network: make erspan netdev can be specified in Network.Tunnel=

src/network/netdev/netdev.c

@@ -779,6 +779,9 @@ int netdev_load_one(Manager *manager, const char *filename) {
         case NETDEV_KIND_IP6TNL:
                 independent = IP6TNL(netdev)->independent;
                 break;
+        case NETDEV_KIND_ERSPAN:
+                independent = ERSPAN(netdev)->independent;
+                break;
         default:
                 break;
         }

src/network/netdev/tunnel.c

@@ -857,6 +857,6 @@ const NetDevVTable erspan_vtable = {
         .init = erspan_init,
         .sections = "Match\0NetDev\0Tunnel\0",
         .fill_message_create = netdev_erspan_fill_message_create,
-        .create_type = NETDEV_CREATE_INDEPENDENT,
+        .create_type = NETDEV_CREATE_STACKED,
         .config_verify = netdev_tunnel_verify,
 };