selftests: mlxsw: ethtool_lanes: Wait for lanes parameter dump explicitly

The ethtool dump includes the lanes parameter only when the port is up.
Therefore, the ethtool_lanes.sh test waits for ports to come before testing
the lanes parameter.

In some cases, the test considers the port as up, but the lanes parameter
is not yet dumped although assumed to be, resulting in ethtool_lanes.sh
test failure.

To avoid that, ensure that the lanes parameter is indeed dumped by waiting
for it explicitly, before preforming the test cases.

Signed-off-by: Danielle Ratson <[e-mail]>
Reviewed-by: Petr Machata <[e-mail]>
Signed-off-by: Petr Machata <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

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

···
 	busywait "$TIMEOUT" wait_for_port_up ethtool $swp2
 	check_err $? "ports did not come up"
 
-	local lanes_exist=$(ethtool $swp1 | grep 'Lanes:')
-	if [[ -z $lanes_exist ]]; then
+	busywait $TIMEOUT sh -c "ethtool $swp1 | grep -q Lanes:"
+	if [[ $? -ne 0 ]]; then
 		log_test "SKIP: driver does not support lanes setting"
 		exit 1
 	fi
···
 			ethtool_set $swp1 speed $max_speed lanes $lanes
 			ip link set dev $swp1 up
 			ip link set dev $swp2 up
-			busywait "$TIMEOUT" wait_for_port_up ethtool $swp2
-			check_err $? "ports did not come up"
+
+			busywait $TIMEOUT sh -c "ethtool $swp1 | grep -q Lanes:"
+			check_err $? "Lanes parameter is not presented on time"
 
 			check_lanes $swp1 $lanes $max_speed
 			log_test "$lanes lanes is autonegotiated"
···
 			ethtool_set $swp2 speed $max_speed lanes $lanes autoneg off
 			ip link set dev $swp1 up
 			ip link set dev $swp2 up
-			busywait "$TIMEOUT" wait_for_port_up ethtool $swp2
-			check_err $? "ports did not come up"
+
+			busywait $TIMEOUT sh -c "ethtool $swp1 | grep -q Lanes:"
+			check_err $? "Lanes parameter is not presented on time"
 
 			check_lanes $swp1 $lanes $max_speed
 			log_test "Autoneg off, $lanes lanes detected during force mode"