QoS: Make outgoing packet processing use CONNMARK

QoS: Make outgoing packet processing use CONNMARK

This will significantly reduce the load when classifying outgoing
traffic as there won't be any overhead as soon as the connection has
been classified. The classficiation is being stored in the iptables MARK
which will be copied to CONNMARK if changed.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>