Core Update 157: Ship backup package to apply changed permissions

This is required as "backup" itself does not gets updated automatically,
contrary to it's LFS file suggesting by having a "PAK_VER" number.

In order to fix #12619, it is therefore necessary to ship the backup
files with Core Update 157.

Partially fixes: #12619

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

diff --git a/config/rootfiles/core/157/filelists/backup b/config/rootfiles/core/157/filelists/backup
new file mode 120000 (symlink)
index 0000000..38e28a8
--- /dev/null
+++ b/config/rootfiles/core/157/filelists/backup
@@ -0,0 +1 @@
+../../../common/backup
\ No newline at end of file