Apply netem packet rules to only UDP traffic (#6754)

scripts/netem.sh

@@ -16,5 +16,14 @@ fi
 set -x
 
 iface="$(ifconfig | grep mtu | grep -iv loopback | grep -i running | awk 'BEGIN { FS = ":" } ; {print $1}')"
+
+if [[ "$1" = delete ]]; then
+  $sudo iptables -F -t mangle
+else
+  $sudo iptables -A POSTROUTING -t mangle -p udp -j MARK --set-mark 1
+fi
+
+$sudo tc qdisc "$1" dev "$iface" root handle 1: prio
 # shellcheck disable=SC2086 # Do not want to quote $2. It has space separated arguments for netem
-$sudo tc qdisc "$1" dev "$iface" root netem $2
+$sudo tc qdisc "$1" dev "$iface" parent 1:3 handle 30: netem $2
+$sudo tc filter "$1" dev "$iface" parent 1:0 protocol ip prio 3 handle 1 fw flowid 1:3