Emit [SUM] output with -P on each iteration

[howardjohn]

iperf output:

[  5]   2.00-2.78   sec  2.19 GBytes  24.1 Gbits/sec    0   1.31 MBytes
[  7]   2.00-2.78   sec  2.19 GBytes  24.1 Gbits/sec    1   1.37 MBytes
[SUM]   2.00-2.78   sec  4.38 GBytes  48.2 Gbits/sec    1
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-2.78   sec  7.98 GBytes  24.6 Gbits/sec    0             sender
[  5]   0.00-2.78   sec  0.00 Bytes  0.00 bits/sec                  receiver
[  7]   0.00-2.78   sec  7.98 GBytes  24.6 Gbits/sec    1             sender
[  7]   0.00-2.78   sec  0.00 Bytes  0.00 bits/sec                  receiver
[SUM]   0.00-2.78   sec  16.0 GBytes  49.3 Gbits/sec    1             sender
[SUM]   0.00-2.78   sec  0.00 Bytes  0.00 bits/sec                  receiver

netperf output:

[  0]   6.00..7.00 sec  5.30 GiB   45.52 Gbits/sec        sender
[  1]   7.00..8.00 sec  5.37 GiB   46.15 Gbits/sec        sender
[  0]   7.00..8.00 sec  5.23 GiB   44.90 Gbits/sec        sender
[  1]   8.00..9.00 sec  4.86 GiB   41.76 Gbits/sec        sender
[  0]   8.00..9.00 sec  4.96 GiB   42.57 Gbits/sec        sender
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
ID   Interval          Transfer      Bitrate
[  0]   0.00..10.00 sec  52.25 GiB   44.88 Gbits/sec        sender
[  0]   0.00..10.00 sec  52.03 GiB   44.69 Gbits/sec        receiver
[  1]   0.00..10.00 sec  51.24 GiB   44.01 Gbits/sec        sender
[  1]   0.00..10.00 sec  51.01 GiB   43.81 Gbits/sec        receiver

[SUM]   0.00..10.00 sec  103.49 GiB   88.89 Gbits/sec        sender
[SUM]   0.00..10.00 sec  103.04 GiB   88.51 Gbits/sec        receiver

You can see netperf only emits the SUM on completion, rather than with each report. Its nice seeing the sum on each report to get a feel for the results before completion.