boards: stm32f4discovery: Add iperf to rndis/defconfig

- NOTE: This commit also removes CONFIG_HOST_WINDOWS=y

nsh> iperf -c 10.0.2.15
       IP: 10.0.2.20

 mode=tcp-client sip=10.0.2.20:5001,dip=10.0.2.15:5001, interval=3, time=30

           Interval         Transfer         Bandwidth

   0.00-   3.01 sec    2211840 Bytes    5.88 Mbits/sec
   3.01-   6.02 sec    4423680 Bytes    5.88 Mbits/sec
   6.02-   9.03 sec    6651904 Bytes    5.92 Mbits/sec
   9.03-  12.04 sec    8863744 Bytes    5.88 Mbits/sec
  12.04-  15.05 sec   11091968 Bytes    5.92 Mbits/sec
  15.05-  18.06 sec   13303808 Bytes    5.88 Mbits/sec
  18.06-  21.07 sec   15532032 Bytes    5.92 Mbits/sec
  21.07-  24.08 sec   17743872 Bytes    5.88 Mbits/sec
  24.08-  27.09 sec   19972096 Bytes    5.92 Mbits/sec
  27.09-  30.10 sec   22183936 Bytes    5.88 Mbits/sec
   0.00-  30.10 sec   22183936 Bytes    5.90 Mbits/sec

nsh> iperf -s
       IP: 10.0.2.20

 mode=tcp-server sip=10.0.2.20:5001,dip=0.0.0.0:5001, interval=3, time=0
accept: 10.0.2.15,59072

           Interval         Transfer         Bandwidth

   0.00-   3.01 sec    1780056 Bytes    4.73 Mbits/sec
   3.01-   6.02 sec    3566544 Bytes    4.75 Mbits/sec
   6.02-   9.03 sec    5350888 Bytes    4.74 Mbits/sec

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

boards/arm/stm32/stm32f4discovery/configs/rndis/defconfig

@@ -32,7 +32,6 @@ CONFIG_FS_FAT=y
 CONFIG_FS_PROCFS=y
 CONFIG_HAVE_CXX=y
 CONFIG_HAVE_CXXINITIALIZE=y
-CONFIG_HOST_WINDOWS=y
 CONFIG_INIT_ENTRYPOINT="nsh_main"
 CONFIG_INIT_STACKSIZE=3072
 CONFIG_INTELHEX_BINARY=y
@@ -49,6 +48,8 @@ CONFIG_NETINIT_NETMASK=0x0
 CONFIG_NETINIT_NOMAC=y
 CONFIG_NETINIT_THREAD=y
 CONFIG_NETUTILS_DHCPC=y
+CONFIG_NETUTILS_IPERF=y
+CONFIG_NETUTILS_IPERFTEST_DEVNAME="eth0"
 CONFIG_NETUTILS_TELNETD=y
 CONFIG_NETUTILS_WEBCLIENT=y
 CONFIG_NET_ARP_SEND=y