link executor: Only create dummy interface when not present.

Signed-off-by: Maximilian Wilhelm <max@sdn.clinic>

executor-scripts/linux/link

@@ -34,6 +34,13 @@ is_vlan() {
 case "$PHASE" in
 pre-up)
 	if [ "${IF_LINK_TYPE}" = "dummy" ]; then
+		if [ -d "/sys/class/net/${IFACE}" ]; then
+			iface_type=$(ip -d link show dev "${IFACE}" | head -n3 | tail -n1 | awk '{ print $1 }')
+			if [ "${iface_type}" = 'dummy' ]; then
+				exit 0
+			fi
+		fi
+
 		ip link add "${IFACE}" type dummy
 	fi
 	;;