[PATCH net] selftests: tc-testing: use $IP in hfsc test 8c39 setup

Test 8c39 brings up lo with a bare "ip" command. nsPlugin runs it as
"$IP netns exec <ns> ip ...", and as tdc runs commands with an empty
environment, "ip netns exec" searches only the default execvp() path
(/bin:/usr/bin). On systems that install ip only in /sbin, like Fedora,
the setup fails:

  # ./tdc.py -e 8c39
  Test 8c39: HFSC classify walk still reaches leaf after lateral drift
  -----> prepare stage *** Could not execute: "ip link set lo up"
  -----> prepare stage *** Error message: "exec of "ip" failed: No such file or directory

Use $IP like all other tdc tests do.

Fixes: 1e24c4f2ee44 ("selftests: tc-testing: add a lateral-drift hfsc classify-walk test")
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
 tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json
index 4f6bbb8b57f9..557730eef055 100644
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/hfsc.json

@@ -181,7 +181,7 @@
             "requires": "nsPlugin"
         },
         "setup": [
-            "ip link set lo up",
+            "$IP link set lo up",
             "$TC qdisc add dev lo handle 1: root hfsc default 30",
             "$TC class add dev lo parent 1: classid 1:1 hfsc rt m2 100kbit",
             "$TC class add dev lo parent 1:1 classid 1:10 hfsc rt m2 50kbit",

-- 
2.56.0