selftests/tc-testing: add selftests for multiq qdisc

selftests/tc-testing: add selftests for multiq qdisc

Test 20ba: Add multiq Qdisc to multi-queue device (8 queues)
Test 4301: List multiq Class
Test 7832: Delete nonexistent multiq Qdisc
Test 2891: Delete multiq Qdisc twice
Test 1329: Add multiq Qdisc to single-queue device

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>