net/sched: sch_qfq: refactor parsing of netlink parameters

Two parameters can be transformed into netlink policies and
validated while parsing the netlink message.

Reviewed-by: Simon Horman <simon.horman@corigine.com>
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>