Support for FQ packet scheduler

$ tc qd add dev eth0 root fq help
Usage: ... fq [ limit PACKETS ] [ flow_limit PACKETS ]
              [ quantum BYTES ] [ initial_quantum BYTES ]
              [ maxrate RATE  ] [ buckets NUMBER ]
              [ [no]pacing ]

$ tc -s -d qd
qdisc fq 8002: dev eth0 root refcnt 32 limit 10000p flow_limit 100p
buckets 256 quantum 3028 initial_quantum 15140
 Sent 216532416 bytes 148395 pkt (dropped 0, overlimits 0 requeues 14)
 backlog 0b 0p requeues 14
  511 flows (511 inactive, 0 throttled)
  110 gc, 0 highprio, 0 retrans, 1143 throttled, 0 flows_plimit

limit	: max number of packets on whole Qdisc (default 10000)

flow_limit : max number of packets per flow (default 100)

quantum : the max deficit per RR round (default is 2 MTU)

initial_quantum : initial credit for new flows (default is 10 MTU)

maxrate : max per flow rate (default : unlimited)

buckets : number of RB trees (default : 1024) in hash table.
               (consumes 8 bytes per bucket)

[no]pacing : disable/enable pacing (default is enable)

Usage :

tc qdisc add dev $ETH root fq

tc qdisc del dev $ETH root 2>/dev/null
tc qdisc add dev $ETH root handle 1: mq
for i in `seq 1 4`
do
  tc qdisc add dev $ETH parent 1:$i est 1sec 4sec fq
done
Signed-off-by: Eric Dumazet <edumazet@google.com>