backup: Add /etc/ipsec.user-post.conf

This file can be manually edited by the user and should be included
in the backup.

Reported-by: Lars Schuhmacher <larsen007@web.de>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

config/backup/include

@@ -9,6 +9,7 @@
 /etc/shadow
 /etc/group
 /etc/ipsec.user.*
+/etc/ipsec.user-post.conf
 /etc/sysconfig/*
 /etc/hosts*
 /etc/httpd/*