since the related code was removed by:
commit 4d5a964f29
Author: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>
Date: Tue Feb 23 18:04:13 2021 +0800
net: unify socket into file descriptor
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Follow the POSIX description.
SIGTSTP should be sent when the Ctrl-Z characters is encountered, not SIGSTP.
Testing:
Built with hifive1-revb:nsh (CONFIG_SERIAL_TERMIOS=y, CONFIG_SIG_DEFAULT=y and CONFIG_TTY_SIGTSTP=y)
