tools, include: Grab a copy of linux/erspan.h

Bring the erspan uapi header file so BPF tunnel helpers can use it.

Fixes: 933a741e ("selftests/bpf: bpf tunnel test.")
Reported-by: Yonghong Song <yhs@fb.com>
Signed-off-by: William Tu <u9012063@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/include/uapi/linux/erspan.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * ERSPAN Tunnel Metadata
+ *
+ * Copyright (c) 2018 VMware
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation.
+ *
+ * Userspace API for metadata mode ERSPAN tunnel
+ */
+#ifndef _UAPI_ERSPAN_H
+#define _UAPI_ERSPAN_H
+
+#include <linux/types.h>	/* For __beXX in userspace */
+#include <asm/byteorder.h>
+
+/* ERSPAN version 2 metadata header */
+struct erspan_md2 {
+	__be32 timestamp;
+	__be16 sgt;	/* security group tag */
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+	__u8	hwid_upper:2,
+		ft:5,
+		p:1;
+	__u8	o:1,
+		gra:2,
+		dir:1,
+		hwid:4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	__u8	p:1,
+		ft:5,
+		hwid_upper:2;
+	__u8	hwid:4,
+		dir:1,
+		gra:2,
+		o:1;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+};
+
+struct erspan_metadata {
+	int version;
+	union {
+		__be32 index;		/* Version 1 (type II)*/
+		struct erspan_md2 md2;	/* Version 2 (type III) */
+	} u;
+};
+
+#endif /* _UAPI_ERSPAN_H */