NR UE: improve PSS detection by reducing the detection step size from 8 to 4

Until commit d74b2bd19f, the PSS detection step size was 4, anyways.
The PSS detection step size is a compromise between detection duration and accuracy.
The most accurate detection step size would be 1, but this would lead to even longer initial sync time.

openair1/PHY/NR_UE_TRANSPORT/pss_nr.c

@@ -560,7 +560,7 @@ static int pss_search_time_nr(const c16_t **rxdata,
   }
 
   for (int pss_index = pss_index_start; pss_index < pss_index_end; pss_index++) {
-    for (n = 0; n < length; n += 8) { //
+    for (n = 0; n < length; n += 4) { //
 
       int64_t pss_corr_ue=0;
       /* calculate dot product of primary_synchro_time_nr and rxdata[ar][n]