backup.pl: Ensure ncp-disable is removed from old backups and DATACIPHERS added

backup.pl: Ensure ncp-disable is removed from old backups and DATACIPHERS added

- With commit https://git.ipfire.org/?p=ipfire-2.x.git;a=commit;h=e04f5376ba18767a6a9eccf104c472295a75340b
   then the settings file which is hashed into %vpnsettings already exists and so none
   of the defaults are set. Running the ovpnmain.cgi code resolves this for most of the
   settings but not for ncp-disable being present in server.conf and no DATACIPHERS entry
   in the settings file. ncp-disable then causes the openvpn server to fail to start as
   it is no longer recognised in OpenVPN-2.6
- This patch checks if ncp-disable is in the server.conf file from the restored backup
   and if it is it is then removed and the default values for DATACIPHERS is added into
   the settings file.
- Tested out in my vm testbed and successfully worked. The previously found issue after
   the above patch was added in has been resolved.
- Associated patch in this set is to do a similar thing for the update.sh file for CU197

Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>