netconf: Skip source routing cfg files when restoring devices

_sortModifiedIfcfgs() uses the cfg files under '/etc/sysconfig/network-scripts'
to get the devices which should be stopped and started during rollback. But the
backed up files could also include source routing cfg files after the source routing
feature was added. So this patch skips those files when it gets the devices list.

Change-Id: I6f72bd29f5f9d4f5d02d8cd2e19675d00eac4600
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/17213
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>