fix(perf): Fix missing UDP iperf title in performance guide

The ethernet performance numbers have a missing title for
ICSSG UDP egress Throughput. Add the title for this missing
section.

Signed-off-by: Meghana Malladi <[email protected]>

Author: MeghanaMalladiTI

source/devices/AM64X/linux/RT_Linux_Performance_Guide.rst

@@ -465,6 +465,9 @@ ICSSG Ethernet Driver
 
     "netperf -H 192.168.2.1 -j -c -C -l 60 -t TCP_STREAM; netperf -H 192.168.2.1 -j -c -C -l 60 -t TCP_MAERTS","359.51","53.51"
 
+.. rubric:: UDP Ingress Throughput
+   :name: ICSSG-udp-ingress-throughput
+
 .. csv-table:: ICSSG UDP Ingress Throughput 0 loss
     :header: "Frame Size(bytes)","am64xx-hsevm: UDP Datagram Size(bytes) (LOCAL_SEND_SIZE)","am64xx-hsevm: THROUGHPUT (Mbits/sec)","am64xx-hsevm: Packets Per Second (kPPS)","am64xx-hsevm: CPU Load %"