networkd: add GatewayOnLink route option

networkd/templates/20-wired-routed.network.j2

@@ -22,6 +22,13 @@ IPForward=yes
 {% if route.gateway is defined %}
 Gateway={{ route.gateway }}
 {% endif %}
+{% if route.gateway_on_link is defined %}
+{% if ansible_distribution_major_version|int <= 10 %}
+GatewayOnlink={{ route.gateway_on_link }}
+{% else %}
+GatewayOnLink={{ route.gateway_on_link }}
+{% endif %}
+{% endif %}
 {% if route.destination is defined %}
 Destination={{ route.destination }}
 {% endif %}