ovl: call secutiry hook in ovl_real_ioctl()

mainline inclusion
from mainline-v5.8-rc1
commit 292f902a
category: bugfix
bugzilla: NA
CVE: CVE-2020-16120

--------------------------------

Verify LSM permissions for underlying file, since vfs_ioctl() doesn't do
it.

[Stephen Rothwell] export security_file_ioctl

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Conflicts:
  fs/overlayfs/file.c
[yyl: adjust context]
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>