selftests/tc-testing: cls_u32: add tests for classid

As discussed in '3044b16e', cls_u32 was handling the use of classid
incorrectly. Add a test to check if it's conforming to the correct
behaviour.
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/tc-testing/tc-tests/filters/u32.json

@@ -247,5 +247,30 @@
         "teardown": [
             "$TC qdisc del dev $DEV1 ingress"
         ]
+    },
+    {
+        "id": "0c37",
+        "name": "Try to delete class referenced by u32 after a replace",
+        "category": [
+            "filter",
+            "u32"
+        ],
+        "plugins": {
+            "requires": "nsPlugin"
+        },
+        "setup": [
+            "$TC qdisc add dev $DEV1 parent root handle 10: drr",
+            "$TC class add dev $DEV1 parent root classid 1 drr",
+            "$TC filter add dev $DEV1 parent 10: prio 1 u32 match icmp type 1 0xff classid 10:1 action ok",
+            "$TC filter replace dev $DEV1 parent 10: prio 1 u32 match icmp type 1 0xff classid 10:1 action drop"
+        ],
+        "cmdUnderTest": "$TC class delete dev $DEV1 parent 10: classid 10:1",
+        "expExitCode": "2",
+        "verifyCmd": "$TC class show dev $DEV1",
+        "matchPattern": "class drr 10:1",
+        "matchCount": "1",
+        "teardown": [
+            "$TC qdisc del dev $DEV1 parent root drr"
+        ]
     }
 ]