selftests: mlxsw: Add a test for leftover DSCP rule

Commit dedfde2f ("mlxsw: spectrum_dcb: Configure DSCP map as the last
rule is removed") fixed a problem in mlxsw where last DSCP rule to be
removed remained in effect when DSCP rewrite was applied.

Add a selftest that covers this problem.
Signed-off-by: NPetr Machata <petrm@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/testing/selftests/drivers/net/mlxsw/qos_dscp_router.sh

@@ -31,6 +31,7 @@ ALL_TESTS="
 	ping_ipv4
 	test_update
 	test_no_update
+	test_dscp_leftover
 "
 
 lib_dir=$(dirname $0)/../../../net/forwarding
@@ -50,6 +51,11 @@ reprioritize()
 	echo ${reprio[$in]}
 }
 
+zero()
+{
+    echo 0
+}
+
 h1_create()
 {
 	simple_if_init $h1 192.0.2.1/28
@@ -225,6 +231,19 @@ test_no_update()
 	__test_update 0 echo
 }
 
+# Test that when the last APP rule is removed, the prio->DSCP map is properly
+# set to zeroes, and that the last APP rule does not stay active in the ASIC.
+test_dscp_leftover()
+{
+	lldptool -T -i $swp2 -V APP -d $(dscp_map 0) >/dev/null
+	lldpad_app_wait_del
+
+	__test_update 0 zero
+
+	lldptool -T -i $swp2 -V APP $(dscp_map 0) >/dev/null
+	lldpad_app_wait_set $swp2
+}
+
 trap cleanup EXIT
 
 setup_prepare