samples: Bluetooth: df: Add use of 16 bits wide IQ sampels

Change implementation of cte_recv_cb to print information about IQ
samples type. The changed code is ready for use of 8 bits and 16 bits
signed integer IQ samples. User has sample level option to enable
printing IQ samples.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>