selftests/tc-testing: add selftests for teql qdisc

Test 84a0: Create TEQL with default setting
Test 7734: Create TEQL with multiple device
Test 34a9: Delete TEQL with valid handle
Test 6289: Show TEQL stats

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>