selftests/tc-testing: add selftests for hfsc qdisc

Test 3254: Create HFSC with default setting
Test 0289: Create HFSC with class sc and ul rate setting
Test 846a: Create HFSC with class sc umax and dmax setting
Test 5413: Create HFSC with class rt and ls rate setting
Test 9312: Create HFSC with class rt umax and dmax setting
Test 6931: Delete HFSC with handle
Test 8436: Show HFSC 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>