fq_codel: return non zero qlen in class dumps

We properly scan the flow list to count number of packets,
but John passed 0 to gnet_stats_copy_queue() so we report
a zero value to user space instead of the result.

Fixes: 64015853 ("net: sched: restrict use of qstats qlen")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: John Fastabend <john.r.fastabend@intel.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>