net_sched: qdisc_get_rtab() must check data[] array

qdisc_get_rtab() should check not only the keys in struct tc_ratespec,
but also the full data[] array.

"tc ... linklayer atm " only perturbs values in the 256 slots array.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>