allow user switch to be used with TCIntf's

this fixes #91

turns out, when the user switch is used without --no-slicing, then it always creates HTB tc queues. therefore, we don't need the different versions of the switch, as I have proposed in #132 for Open vSwitch.

the code here, while closely following the design for `TCReapply` for Open vSwitch, is subtly different, since the user switch configures different class numbers than OVS, and we don't have access to the link speed via ovs-vsctl.