selftests: mlxsw: hw_stats_l3: Add a new test

Add a test that verifies that UAPI notifications are emitted, as mlxsw
installs and deinstalls HW counters for the L3 offload xstats.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

tools/testing/selftests/drivers/net/mlxsw/hw_stats_l3.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+lib_dir=$(dirname $0)/../../../net/forwarding
+
+ALL_TESTS="
+	l3_monitor_test
+"
+NUM_NETIFS=0
+source $lib_dir/lib.sh
+
+swp=$NETIF_NO_CABLE
+
+cleanup()
+{
+	pre_cleanup
+}
+
+l3_monitor_test()
+{
+	hw_stats_monitor_test $swp l3		    \
+		"ip addr add dev $swp 192.0.2.1/28" \
+		"ip addr del dev $swp 192.0.2.1/28"
+}
+
+trap cleanup EXIT
+
+setup_wait
+tests_run
+
+exit $EXIT_STATUS