missing: support old linux/fou.h

linux/fou.h was introduced in 3.18.
FOU_ATTR_REMCSUM_NOPARTIAL was added in 4.0.
FOU_CMD_GET was added in 4.1.

Follow-up for 53cb501a13.
Fixes #10474.

src/network/netdev/fou-tunnel.h

@@ -1,11 +1,12 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 #pragma once
 
-#if HAVE_FOU_CMD_GET
+#if HAVE_LINUX_FOU_H
 #include <linux/fou.h>
 #endif
 
 #include "in-addr-util.h"
+#include "missing.h"
 #include "netdev/netdev.h"
 
 typedef enum FooOverUDPEncapType {

src/network/netdev/tunnel.c

@@ -6,12 +6,12 @@
 #include <linux/if_tunnel.h>
 #include <linux/ip6_tunnel.h>
 
-#include "sd-netlink.h"
-
-#if HAVE_FOU_CMD_GET
+#if HAVE_LINUX_FOU_H
 #include <linux/fou.h>
 #endif
 
+#include "sd-netlink.h"
+
 #include "conf-parser.h"
 #include "missing.h"
 #include "networkd-link.h"