DVB-S[2] uses a rolloff factor, not hierachy

Currently, TV-Headend assumes that the 5th field is hierachy. This is
incorrect, the 5th field in a scanfile for DVB-S[2] is rolloff.

This patch adds support for rolloff on scan and sets it approperatly.

Signed-off-by: Oliver Schinagl <oliver@schinagl.nl>