selftests/tc-testing: add selftests for drr qdisc

Test 0385: Create DRR with default setting
Test 2375: Delete DRR with handle
Test 3092: Show DRR class

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>