qosify: keep ICMP in the default best-effort class

Also preserve existing DSCP tags to make it easier to test latency for
different DSCP values

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/network/config/qosify/files/qosify.conf

@@ -1,7 +1,7 @@
 config defaults
 	list defaults /etc/qosify/*.conf
 	option dscp_prio CS5
-	option dscp_icmp CS6
+	option dscp_icmp +CS0
 	option dscp_bulk bulk
 	option dscp_default_udp	CS4
 	option bulk_trigger_timeout 5