Reduce iperf throughput in 5G F1 RFsim test

The next commit adds channel emulation in RFsim, so we have to reduce
the iperf, as the machine might not be fast enough.

ci-scripts/xml_files/container_5g_f1_rfsim.xml

@@ -76,8 +76,8 @@
 
         <testCase id="030021">
                 <class>Iperf</class>
-                <desc>Iperf (DL/20Mbps/UDP)(30 sec)</desc>
-                <iperf_args>-u -b 20M -t 30 -R</iperf_args>
+                <desc>Iperf (DL/5Mbps/UDP)(30 sec)</desc>
+                <iperf_args>-u -b 5M -t 30 -R</iperf_args>
                 <id>rfsim5g_ue</id>
                 <svr_id>rfsim5g_ext_dn</svr_id>
                 <iperf_packetloss_threshold>5</iperf_packetloss_threshold>
@@ -86,8 +86,8 @@
 
         <testCase id="030022">
                 <class>Iperf</class>
-                <desc>Iperf (UL/5Mbps/UDP)(30 sec)</desc>
-                <iperf_args>-u -b 5M -t 30</iperf_args>
+                <desc>Iperf (UL/3Mbps/UDP)(30 sec)</desc>
+                <iperf_args>-u -b 3M -t 30</iperf_args>
                 <id>rfsim5g_ue</id>
                 <svr_id>rfsim5g_ext_dn</svr_id>
                 <iperf_packetloss_threshold>5</iperf_packetloss_threshold>