Always use bi-direction target communication

Always use bi-direction target communication

I don't remember what was the reason for setting up bi-directional
interaction only when on terminal. It seems, it is useful to have also
when not on terminal - for example when running under socat.

With this change, I'm able to use novaboot with socat to load u-boot
to the target using X-modem protocol:

    socat EXEC:"novaboot -t mytarget --no-uboot --no-reset /dev/null" EXEC:"sx -kbvv -t 10 ./images/u-boot-spl.bin"