Test tc filter based priority sorting for PPPoE encapsulated traffic

iptables do not have access to inner headers of passing PPPoE
encapsulated packets. Create a special set of tc filters to
inspect the content of PPPoE packets. While work in progress this does allow
to use the SQM router as PPPoE termination pint yet set up SQM on
the ethernet interface instead of the pppoe interface, and yet keep
decent classification intact. Currently classification is only
working for IPv4 egress traffic. WIP...
Implement initial classification of egress IPv6 PPPoE packets

This change corrects the tc filter mask for the IPv6 Traffic class field
Now egress classification also works for IPv6.