tc: fq: add horizon attributes

tc: fq: add horizon attributes

Commit 39d010504e6b ("net_sched: sch_fq: add horizon attribute")
added kernel support for horizon attributes in linux-5.8

$ tc -s -d qd sh dev wlp2s0
qdisc fq 8006: root refcnt 2 limit 10000p flow_limit 100p buckets 1024 orphan_mask 1023 quantum 3028b initial_quantum 15140b low_rate_threshold 550Kbit refill_delay 40ms timer_slack 10us horizon 10s horizon_drop
 Sent 690924 bytes 3234 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
  flows 112 (inactive 104 throttled 0)
  gc 0 highprio 0 throttled 2 latency 8.25us

$ tc qd change dev wlp2s0 root fq horizon 500ms horizon_cap

$ tc -s -d qd sh dev wlp2s0
qdisc fq 8006: root refcnt 2 limit 10000p flow_limit 100p buckets 1024 orphan_mask 1023 quantum 3028b initial_quantum 15140b low_rate_threshold 550Kbit refill_delay 40ms timer_slack 10us horizon 500ms horizon_cap
 Sent 831220 bytes 3844 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
  flows 122 (inactive 120 throttled 0)
  gc 0 highprio 0 throttled 2 latency 8.25us

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David Ahern <dsahern@kernel.org>