Mesh range testing

@rickkas7 can you point me in the right direction of how to do a monolithic build to get RSSI code like this running on an Xenon or Argon?

#if MODULE_FUNCTION == 3
// This is a monolithic build, so we have RSSI functions available
#define HAS_RSSI
#include "ot_api.h"
extern "C" {
int8_t otPlatRadioGetRssi(otInstance *aInstance);
};
#endif

#ifdef HAS_RSSI
int8_t rssi = otPlatRadioGetRssi(0);
snprintf(buf, sizeof(buf), "rssi %d", (int)rssi);
display.println(buf);
#endif