support for Heavy Hitter Filter (HHF) qdisc

support for Heavy Hitter Filter (HHF) qdisc

$tc qdisc add dev eth0 hhf help
Usage: ... hhf [ limit PACKETS ] [ quantum BYTES]
               [ hh_limit NUMBER ]
               [ reset_timeout TIME ]
               [ admit_bytes BYTES ]
               [ evict_timeout TIME ]
               [ non_hh_weight NUMBER ]

$tc -s -d qdisc show dev eth0
qdisc hhf 8005: root refcnt 32 limit 1000p quantum 1514 hh_limit 2048
reset_timeout 40.0ms admit_bytes 131072 evict_timeout 1.0s non_hh_weight 2
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
  backlog 0b 0p requeues 0
    drop_overlimit 0 hh_overlimit 0 tot_hh 0 cur_hh 0

HHF qdisc parameters:
- limit: max number of packets in qdisc (default 1000)
- quantum: max deficit per RR round (default 1 MTU)
- hh_limit: max number of HHs to keep states (default 2048)
- reset_timeout: time to reset HHF counters (default 40ms)
- admit_bytes: counter thresh to classify as HH (default 128KB)
- evict_timeout: threshold to evict idle HHs (default 1s)
- non_hh_weight:  DRR weight for mice (default 2)

Signed-off-by: Terry Lam <vtlam@google.com>