selftests: mlxsw: tc_police_scale: Make test more robust

The test adds tc filters and checks how many of them were offloaded by
grepping for 'in_hw'.

iproute2 commit f4cd4f127047 ("tc: add skip_hw and skip_sw to control
action offload") added offload indication to tc actions, producing the
following output:

 $ tc filter show dev swp2 ingress
 ...
 filter protocol ipv6 pref 1000 flower chain 0 handle 0x7c0
   eth_type ipv6
   dst_ip 2001:db8:1::7bf
   skip_sw
   in_hw in_hw_count 1
         action order 1:  police 0x7c0 rate 10Mbit burst 100Kb mtu 2Kb action drop overhead 0b
         ref 1 bind 1
         not_in_hw
         used_hw_stats immediate

The current grep expression matches on both 'in_hw' and 'not_in_hw',
resulting in incorrect results.

Fix that by using JSON output instead.

Fixes: 5061e77 ("selftests: mlxsw: Add scale test for tc-police")
Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/mlxsw/tc_police_scale.sh

@@ -60,7 +60,8 @@ __tc_police_test()
 
  tc_police_rules_create $count $should_fail
 
- offload_count=$(tc filter show dev $swp1 ingress | grep in_hw | wc -l)
+ offload_count=$(tc -j filter show dev $swp1 ingress |
+ jq "[.[] | select(.options.in_hw == true)] | length")
  ((offload_count == count))
  check_err_fail $should_fail $? "tc police offload count"
 }