net/tcp: add kconfig to support retransmission at a fixed time

[zhhyu7]

Summary

the maximum retransmission interval allowed for car projects cannot exceed 6 seconds, and allows for fixed retransmission intervals. according to the previous algorithm, the retransmission interval may be 0.5 * 2 ^ 4 = 8 seconds, which does not meet the requirements.

Impact

retransmission Time Strategy for TCP Network Communication.

Testing

sim:matter with iperf
test log

NuttShell (NSH) NuttX-12.11.0
MOTD: username=admin password=Administrator
nsh> iperf -c 10.0.1.1 -B 10.0.1.2
     IP: 10.0.1.2

 mode=tcp-client sip=10.0.1.2:5001,dip=10.0.1.1:5001, interval=3, time=30

           Interval         Transfer         Bandwidth

   0.00-   3.08 sec  189693952 Bytes  492.71 Mbits/sec
   3.08-   8.89 sec  359940096 Bytes  495.61 Mbits/sec
   8.89-  11.96 sec  190152704 Bytes  495.51 Mbits/sec
  11.96-  16.11 sec  254279680 Bytes  490.18 Mbits/sec
  16.11-  22.52 sec  388710400 Bytes  485.13 Mbits/sec
  22.52-  25.78 sec  200228864 Bytes  491.36 Mbits/sec
  25.78-  31.58 sec  347570176 Bytes  479.41 Mbits/sec
   0.00-  31.58 sec 1946484736 Bytes  493.09 Mbits/sec
iperf exit
nsh> poweroff
[Inferior 1 (process 3015966) exited normally]
(gdb) q
nuttx$ cat .config | grep DROP
# CONFIG_NET_TCP_DEBUG_DROP_RECV is not set
CONFIG_NET_TCP_DEBUG_DROP_SEND=y
CONFIG_NET_TCP_DEBUG_DROP_SEND_PROBABILITY=50
nuttx$ cat .config | grep FIXED
CONFIG_NET_TCP_FIXED_RTO=y
# CONFIG_MBEDTLS_ECP_FIXED_POINT_OPTIM is not set

[acassis]

@zhhyu7 please update the Kconfig help (many users will not know that RTO means ReTransmission timeOut) and please add a note in the Documentation to explain that now it is supported.

fixed