tc-testing: Add control-plane selftests for sch_mq

Recently we added multi-queue support to netdevsim in commit d4861fc6
("netdevsim: Add multi-queue support"); add a few control-plane selftests
for sch_mq using this new feature.

Use nsPlugin.py to avoid network interface name collisions.

Reviewed-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Signed-off-by: David S. Miller <davem@davemloft.net>