qos-scripts: fix ingress packet marking with ifb

Split connection mark into two parts:

The lower nibble contains the confirmed conntrack mark which is not
generated by default/reclassify rules.
The upper nibble contains the current value specified by
default/reclassify rules.

For egress, the default/reclassify value is preferred
For ingress, the connection mark is preferred

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@41682 3c298f89-4303-0410-b956-a3cf2f4a3e73