The numeric value '3' for the ASCII character CTRL-C is not immediately readable, even if the lines that follow explicitly mention CTRL-C. Use the same macro present in `telnet_server.c` to replace the numeric value. Change-Id: Iaf4296b1f0e384f8122d8a4875cad17e8ddaf66a Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com> Reviewed-on: https://review.openocd.org/c/openocd/+/8922 Reviewed-by: Tomas Vanek <vanekt@fbl.cz> Tested-by: jenkins