selftests: tc-testing: add more tests for sch_qfq

The QFQ qdisc class has parameter bounds that are not being
checked for correctness.

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>