tc-testing: add simple action change test

Use act_simple to verify that action created with 'tc actions change'
command exists after command returns. The goal is to verify internal action
API reference counting to ensure that the case when netlink message has
NLM_F_REPLACE flag set but action with specified index doesn't exist is
handled correctly.
Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/tc-testing/tc-tests/actions/simple.json

@@ -23,6 +23,30 @@
             "$TC actions flush action simple"
         ]
     },
+    {
+        "id": "4297",
+        "name": "Add simple action with change command",
+        "category": [
+            "actions",
+            "simple"
+        ],
+        "setup": [
+            [
+                "$TC actions flush action simple",
+                0,
+                1,
+                255
+            ]
+        ],
+        "cmdUnderTest": "$TC actions change action simple sdata \"Not changed\" index 60",
+        "expExitCode": "0",
+        "verifyCmd": "$TC actions list action simple",
+        "matchPattern": "action order [0-9]*: Simple <Not changed>.*index 60 ref",
+        "matchCount": "1",
+        "teardown": [
+            "$TC actions flush action simple"
+        ]
+    },
     {
         "id": "6d4c",
         "name": "Add simple action with duplicate index",