The commit 9aaa3b8b ("thunderbolt: Add support for preboot ACL")
introduced boot_acl attribute but missed the fact that now userspace
needs to poll the attribute constantly to find out whether it has
changed or not. Fix this by sending notification to the userspace
whenever the boot_acl attribute is changed.

Fixes: 9aaa3b8b ("thunderbolt: Add support for preboot ACL")
Reported-and-tested-by: Christian Kellner <christian@kellner.me>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Christian Kellner <christian@kellner.me>
Acked-by: Yehezkel Bernat <yehezkelshb@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>