drivers/xbee: disable CTS/RTS pin unless periph_uart_hw_fc is used
drivers/xbee: disable CTS/RTS pin unless periph_uart_hw_fc is used

If usinng an arduino xbee shield then CTS pin will be wired to the
ICSP connector RESET pin.

If also used on an arduino-% board then if xbee is busy sending or
receiving data it will assert CTS and this will trigger a reset on
the board.

To avoid this disable CTS functionality on start up unless hardware
flow control is explicitly requested.

kaspar030/RIOT,basilfx/RIOT,jasonatran/RIOT,OlegHahm/RIOT,kYc0o/RIOT,ant9000/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,authmillenon/RIOT,authmillenon/RIOT,basilfx/RIOT,OTAkeys/RIOT,miri64/RIOT,authmillenon/RIOT,ant9000/RIOT,basilfx/RIOT,miri64/RIOT,jasonatran/RIOT,OlegHahm/RIOT,basilfx/RIOT,kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,miri64/RIOT,jasonatran/RIOT,ant9000/RIOT,basilfx/RIOT,jasonatran/RIOT,authmillenon/RIOT,ant9000/RIOT,miri64/RIOT,kYc0o/RIOT,jasonatran/RIOT,kaspar030/RIOT,kaspar030/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,miri64/RIOT,OTAkeys/RIOT,ant9000/RIOT,OTAkeys/RIOT,kYc0o/RIOT