selftests/tc-testing: add selftests for netem qdisc

selftests/tc-testing: add selftests for netem qdisc

Test cb28: Create NETEM with default setting
Test a089: Create NETEM with limit flag
Test 3449: Create NETEM with delay time
Test 3782: Create NETEM with distribution and corrupt flag
Test 2b82: Create NETEM with distribution and duplicate flag
Test a932: Create NETEM with distribution and loss flag
Test e01a: Create NETEM with distribution and loss state flag
Test ba29: Create NETEM with loss gemodel flag
Test 0492: Create NETEM with reorder flag
Test 7862: Create NETEM with rate limit
Test 7235: Create NETEM with multiple slot rate
Test 5439: Create NETEM with multiple slot setting
Test 5029: Change NETEM with loss state
Test 3785: Replace NETEM with delay time
Test 4502: Delete NETEM with handle
Test 0785: Show NETEM 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>