QoS: Use CONNMARK to mark connections in connection tracking

QoS: Use CONNMARK to mark connections in connection tracking

This patch modifies the connection tracking in that ways that
it sets a connection mark which will be retrieved when a packet
is being redirected to the IFB interface.

This way, we can use classification without having the packet
being sent through iptables first.

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