selftests: forwarding: router_mpath_nh_lib: Don't skip, xfail on veth

When the NH group stats tests are currently run on a veth topology, the
HW-stats leg of each test is SKIP'ped. But kernel networking CI interprets
skips as a sign that tooling is missing, and prompts maintainer
investigation. Lack of capability to pass a test should be expressed as
XFAIL.

Selftests that require HW should normally be put in drivers/net/hw, but
doing so for the NH counter selftests would just lead to a lot of
duplicity.

So instead, introduce a helper, xfail_on_veth(), which can be used to mark
selftests that should XFAIL instead of FAILing when run on a veth topology.
On non-veth topology, they don't do anything.

Use the helper in the HW-stats part of router_mpath_nh_lib selftest.

Signed-off-by: Petr Machata <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/net/forwarding/lib.sh

···
 	fi
 }
 
+xfail_on_veth()
+{
+	local dev=$1; shift
+	local kind
+
+	kind=$(ip -j -d link show dev $dev |
+			jq -r '.[].linkinfo.info_kind')
+	if [[ $kind = veth ]]; then
+		FAIL_TO_XFAIL=yes "$@"
+	else
+		"$@"
+	fi
+}
+
 log_test_result()
 {
 	local test_name=$1; shift

tools/testing/selftests/net/forwarding/router_mpath_nh_lib.sh

···
 	local group_id=$1; shift
 	local mz="$@"
 
-	local used
-
 	nh_stats_do_test "$what" "$nh1_id" "$nh2_id" "$group_id" \
 			 nh_stats_get "${mz[@]}"
 
-	used=$(ip -s -j -d nexthop show id $group_id |
-		   jq '.[].hw_stats.used')
-	kind=$(ip -j -d link show dev $rp11 |
-		   jq -r '.[].linkinfo.info_kind')
-	if [[ $used == true ]]; then
+	xfail_on_veth $rp11 \
 		nh_stats_do_test "HW $what" "$nh1_id" "$nh2_id" "$group_id" \
 				 nh_stats_get_hw "${mz[@]}"
-	elif [[ $kind == veth ]]; then
-		log_test_xfail "HW stats not offloaded on veth topology"
-	fi
 }
 
 nh_stats_test_dispatch()
···
 	local mz="$@"
 
 	local enabled
-	local kind
 
 	if ! ip nexthop help 2>&1 | grep -q hw_stats; then
 		log_test_skip "NH stats test: ip doesn't support HW stats"