[tc] Allow deleting root qdisc

ipr.tc(RTM_DELQDISC, None, ethid, 0, parent=TC_H_ROOT)
provide the same functionality as:
tc qdisc del dev eth0 root

IPRoute.tc method should account for an undefined TC_KIND. This allows
deleting the root QDisc
Merge pull request #19 from chantra/del_root_qdisc

[tc] Allow deleting root qdisc