XON/XOFF hardcoded in sio.c and sio_poll.c

[emard]

8-bit clean stream is needed. please remove XON/XOFF
from library or at least let it not be default

[emard]

but I found out that sio.c and sio_poll.c are not used in arduino,
it has its own serial class and has by default enabled xon/xoff
what can be disabled with this:

Serial.setXoffXon(FALSE);