Move samples of int16_t format to sample_t, that is of type double

This prepares the correction of all levels

src/common/display_iq.c

@@ -21,6 +21,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <math.h>
+#include "sample.h"
 #include "sender.h"
 
 #define DISPLAY_INTERVAL 0.04