Reduce indentation, add comment

Reduce one level of indentation, and explain why we wait for
physide_dl_tti callback.

radio/fhi_72/oaioran.c

@@ -112,7 +112,11 @@ void oai_xran_fh_rx_callback(void *pCallbackTag, xran_status_t status)
       }
     }
 #endif
-    if (first_call_set) {
+    // if xran did not call xran_physide_dl_tti callback, it's not ready yet.
+    // wait till first callback to advance counters, because otherwise users
+    // would see periodic output with only "0" in stats counters
+    if (!first_call_set)
+      return;
     slot2 = slot + (subframe * slots_per_subframe);
     rx_RU[ru_id][slot2] = 1;
     if (last_frame > 0 && frame > 0
@@ -144,7 +148,6 @@ void oai_xran_fh_rx_callback(void *pCallbackTag, xran_status_t status)
       LOG_E(PHY, "Cannot Push %d.%d.%d (slot %d, subframe %d,last_slot %d)\n", frame, slot2, ru_id, slot, subframe, last_slot);
     last_slot = slot2;
     last_frame = frame;
-    } // first_call_set
   } // rx_sym == 7
 }
 void oai_xran_fh_srs_callback(void *pCallbackTag, xran_status_t status)