Fix integer overflow

Avoid UBSan error:
  openair1/PHY/NR_ESTIMATION/nr_measurements_gNB.c:246:18: runtime error: signed integer overflow: 1457321472 + 922889664 cannot be represented in type 'int'

openair1/PHY/NR_ESTIMATION/nr_measurements_gNB.c

@@ -203,7 +203,7 @@ void nr_gnb_measurements(PHY_VARS_gNB *gNB,
                          unsigned char symbol,
                          uint8_t nrOfLayers)
 {
-  int rx_power_tot = 0;
+  uint32_t rx_power_tot = 0;
   unsigned short rx_power_avg_dB;
   unsigned short rx_power_tot_dB;
   RU_t *ru = gNB->RU_list[0];