Revert vendor directory to support old golang (GOPATH mode)

gomodule is still in progress to migrate for now, hence multus
team decide to keep vendor directory to support build without
gomodule.

vendor/golang.org/x/sys/unix/openbsd_unveil.go

@@ -0,0 +1,44 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build openbsd
+
+package unix
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// Unveil implements the unveil syscall.
+// For more information see unveil(2).
+// Note that the special case of blocking further
+// unveil calls is handled by UnveilBlock.
+func Unveil(path string, flags string) error {
+	pathPtr, err := syscall.BytePtrFromString(path)
+	if err != nil {
+		return err
+	}
+	flagsPtr, err := syscall.BytePtrFromString(flags)
+	if err != nil {
+		return err
+	}
+	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(unsafe.Pointer(pathPtr)), uintptr(unsafe.Pointer(flagsPtr)), 0)
+	if e != 0 {
+		return e
+	}
+	return nil
+}
+
+// UnveilBlock blocks future unveil calls.
+// For more information see unveil(2).
+func UnveilBlock() error {
+	// Both pointers must be nil.
+	var pathUnsafe, flagsUnsafe unsafe.Pointer
+	_, _, e := syscall.Syscall(SYS_UNVEIL, uintptr(pathUnsafe), uintptr(flagsUnsafe), 0)
+	if e != 0 {
+		return e
+	}
+	return nil
+}