selftests/tc-testing: add selftests for cake qdisc

Test 1212: Create CAKE with default setting
Test 3281: Create CAKE with bandwidth limit
Test c940: Create CAKE with autorate-ingress flag
Test 2310: Create CAKE with rtt time
Test 2385: Create CAKE with besteffort flag
Test a032: Create CAKE with diffserv8 flag
Test 2349: Create CAKE with diffserv4 flag
Test 8472: Create CAKE with flowblind flag
Test 2341: Create CAKE with dsthost and nat flag
Test 5134: Create CAKE with wash flag
Test 2302: Create CAKE with flowblind and no-split-gso flag
Test 0768: Create CAKE with dual-srchost and ack-filter flag
Test 0238: Create CAKE with dual-dsthost and ack-filter-aggressive flag
Test 6572: Create CAKE with memlimit and ptm flag
Test 2436: Create CAKE with fwmark and atm flag
Test 3984: Create CAKE with overhead and mpu
Test 5421: Create CAKE with conservative and ingress flag
Test 6854: Delete CAKE with conservative and ingress flag
Test 2342: Replace CAKE with mpu
Test 2313: Change CAKE with mpu
Test 4365: Show CAKE class
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>