selftests: rtnetlink: check enslaving iface in a bond

The goal is to check the following two sequences:
> ip link set dummy0 up
> ip link set dummy0 master bond0 down
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240108094103.2001224-3-nicolas.dichtel@6wind.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/rtnetlink.sh

@@ -28,6 +28,7 @@ ALL_TESTS="
 	kci_test_neigh_get
 	kci_test_bridge_parent_id
 	kci_test_address_proto
+	kci_test_enslave_bonding
 "
 
 devdummy="test-dummy0"
@@ -1241,6 +1242,33 @@ kci_test_address_proto()
 	return $ret
 }
 
+kci_test_enslave_bonding()
+{
+	local testns="testns"
+	local bond="bond123"
+	local dummy="dummy123"
+	local ret=0
+
+	run_cmd ip netns add "$testns"
+	if [ $ret -ne 0 ]; then
+		end_test "SKIP bonding tests: cannot add net namespace $testns"
+		return $ksft_skip
+	fi
+
+	run_cmd ip -netns $testns link add dev $bond type bond mode balance-rr
+	run_cmd ip -netns $testns link add dev $dummy type dummy
+	run_cmd ip -netns $testns link set dev $dummy up
+	run_cmd ip -netns $testns link set dev $dummy master $bond down
+	if [ $ret -ne 0 ]; then
+		end_test "FAIL: initially up interface added to a bond and set down"
+		ip netns del "$testns"
+		return 1
+	fi
+
+	end_test "PASS: enslave interface in a bond"
+	ip netns del "$testns"
+}
+
 kci_test_rtnl()
 {
 	local current_test