selftests/tc-testing: update test definitions for local resources

With resources localized on a per test basis, some tests definitions
either contain redundant commands, were wrong or could be simplified.
Update all of them to match the new requirements.

Tested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

selftests/tc-testing: add selftests for skbprio qdisc

Test 283e: Create skbprio with default setting
Test c086: Create skbprio with limit setting
Test 6733: Change skbprio with limit setting
Test 2958: Show skbprio class

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