selftests: net/forwarding: test purge of active DWRR classes

Extend sch_ets.sh to add a reproducer for problematic list deletions when
active DWRR class are purged by ets_qdisc_change() [1] [2].

[1] https://lore.kernel.org/netdev/e08c7f4a6882f260011909a868311c6e9b54f3e4.1639153474.git.dcaratti@redhat.com/
[2] https://lore.kernel.org/netdev/f3b9bacc73145f265c19ab80785933da5b7cbdec.1754581577.git.dcaratti@redhat.com/

Suggested-by: Victor Nogueira <[email protected]>
Signed-off-by: Davide Caratti <[email protected]>
Acked-by: Victor Nogueira <[email protected]>
Link: https://patch.msgid.link/489497cb781af7389011ca1591fb702a7391f5e7.1755016081.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <[email protected]>

Author: dcaratti

tools/testing/selftests/net/forwarding/sch_ets.sh

@@ -11,6 +11,7 @@ ALL_TESTS="
 	ets_test_strict
 	ets_test_mixed
 	ets_test_dwrr
+	ets_test_plug
 	classifier_mode
 	ets_test_strict
 	ets_test_mixed

tools/testing/selftests/net/forwarding/sch_ets_tests.sh

@@ -224,3 +224,11 @@ ets_test_dwrr()
 	ets_set_dwrr_two_bands
 	xfail_on_slow ets_dwrr_test_01
 }
+
+ets_test_plug()
+{
+	ets_change_qdisc $put 2 "3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3" "1514 1514"
+	tc qdisc add dev $put handle 20: parent 10:4 plug
+	start_traffic_pktsize 100 $h1.10 192.0.2.1 192.0.2.2 00:c1:a0:c1:a0:00 "-c 1"
+	ets_qdisc_setup $put 2
+}