Keep track of number of RUs in L1

Need to keep track of number of RUs, as the RU initialization increments
the number of RUs. Therefore, subsequent initializations would fail if
we don't decrement first. There is no better place (or I did not find
it) to decrement the number of RUs than in nr_phy_free_RU(). For this
reason, we also have to manually set the number of RUs in nr_prachsim to
1, otherwise the assert will trigger.

openair1/PHY/INIT/nr_init_ru.c

@@ -180,4 +180,8 @@ void nr_phy_free_RU(RU_t *ru)
       free_and_zero(ru->common.beam_id[i]);
     free_and_zero(ru->common.beam_id);
   }
+
+  PHY_VARS_gNB *gNB0 = ru->gNB_list[0];
+  gNB0->num_RU--;
+  DevAssert(gNB0->num_RU >= 0);
 }

openair1/SIMULATION/NR_PHY/prachsim.c

@@ -467,6 +467,7 @@ int main(int argc, char **argv){
   ru->nb_rx          = n_rx;
   ru->num_gNB        = 1;
   ru->gNB_list[0]    = gNB;
+  gNB->num_RU = 1;
   gNB->gNB_config.carrier_config.num_tx_ant.value = 1;
   gNB->gNB_config.carrier_config.num_rx_ant.value = 1;
   if (mu == 0)