ovpn-dco: include new GSO header file

GSO code has ben moved to its own files, therefore a new header
needs to be included accordingly.

This patch also provides some compat files so that ovpn-dco can
continue to compile also on older kernels.

Fixes: #42
Signed-off-by: Antonio Quartulli <antonio@openvpn.net>

Makefile

@@ -34,8 +34,8 @@ ELFLAG := $(EL8FLAG) $(EL9FLAG)
 NOSTDINC_FLAGS += \
 	-I$(PWD)/include/ \
 	$(CFLAGS) $(ELFLAG) \
-	-include $(PWD)/linux-compat.h
-#	-I$(PWD)/compat-include/
+	-include $(PWD)/linux-compat.h \
+	-I$(PWD)/compat-include/
 
 ifneq ($(REVISION),)
 NOSTDINC_FLAGS += -DOVPN_DCO_VERSION=\"$(REVISION)\"

compat-include/net/gso.h

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* OpenVPN data channel accelerator
+ *
+ *  Copyright (C) 2023 OpenVPN, Inc.
+ *
+ *  Author:	Antonio Quartulli <antonio@openvpn.net>
+ */
+
+#ifndef _NET_OVPN_COMPAT_NET_GSO_H
+#define _NET_OVPN_COMPAT_NET_GSO_H
+
+#include <linux/version.h>
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 4, 10)
+#include_next <net/gso.h>
+#else
+#include <linux/netdevice.h>
+#endif
+
+#endif /* _NET_OVPN_COMPAT_NET_GSO_H */

drivers/net/ovpn-dco/ovpn.c

@@ -22,6 +22,7 @@
 #include "udp.h"
 
 #include <linux/workqueue.h>
+#include <net/gso.h>
 #include <uapi/linux/if_ether.h>
 
 static const unsigned char ovpn_keepalive_message[] = {