tc filters: add support to get individual filters by handle

tc filters: add support to get individual filters by handle

sudo $TC filter add dev $ETH parent ffff: prio 2 protocol ip \
u32 match u32 0 0 flowid 1:1 \
action ok
sudo $TC filter add dev $ETH parent ffff: prio 1 protocol ip \
u32 match ip protocol 1 0xff flowid 1:10 \
action ok

now dump to see all rules..
$TC -s filter ls dev $ETH parent ffff: protocol ip
 ....
filter pref 1 u32
filter pref 1 u32 fh 801: ht divisor 1
filter pref 1 u32 fh 801::800 order 2048 key ht 801 bkt 0 flowid 1:10  (rule hit 0 success 0)
  match 00010000/00ff0000 at 8 (success 0 )
        action order 1: gact action drop
         random type none pass val 0
         index 6 ref 1 bind 1 installed 4 sec used 4 sec
        Action statistics:
        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

filter pref 2 u32
filter pref 2 u32 fh 800: ht divisor 1
filter pref 2 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1  (rule hit 336 success 336)
  match 00000000/00000000 at 0 (success 336 )
        action order 1: gact action pass
         random type none pass val 0
         index 5 ref 1 bind 1 installed 38 sec used 4 sec
        Action statistics:
        Sent 24864 bytes 336 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0
 ....

..get filter 801::800
$TC -s filter get dev $ETH parent ffff: protocol ip \
handle 801:0:800 prio 2  u32

 ....
filter parent ffff: protocol ip pref 1 u32 fh 801::800 order 2048 key ht 801 bkt 0 flowid 1:10  (rule hit 260 success 130)
  match 00010000/00ff0000 at 8 (success 130 )
        action order 1: gact action drop
         random type none pass val 0
         index 6 ref 1 bind 1 installed 348 sec used 0 sec
        Action statistics:
        Sent 11440 bytes 130 pkt (dropped 130, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0
 ....

..get other one
$TC -s filter get dev $ETH parent ffff: protocol ip \
handle 800:0:800 prio 2  u32

....
filter parent ffff: protocol ip pref 2 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1  (rule hit 514 success 514)
  match 00000000/00000000 at 0 (success 514 )
        action order 1: gact action pass
         random type none pass val 0
         index 5 ref 1 bind 1 installed 506 sec used 4 sec
        Action statistics:
        Sent 35544 bytes 514 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0
....

..try something that doesnt exist
$TC -s filter get dev $ETH parent ffff: protocol ip  handle 800:0:803 prio 2  u32

.....
RTNETLINK answers: No such file or directory
We have an error talking to the kernel
.....

Note, added NLM_F_ECHO is for backward compatibility. old kernels never
before Eric's patch will not respond without it and newer kernels (after Erics patch)
will ignore it.
In old kernels there is a side effect:
In addition to a response to the GET you will receive an event (if you do tc mon).
But this is still better than what it was before (not working at all).

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>