Allow to use multiple PUCCH at once

We are required to store multiple PUCCH (e.g., for multiple UEs).
However, nr_fill_pucch() automatically freed the previously active PUCCH
structure. Of course(!) this does not make sense.

However, the problem is that init_nr_transport() allocated only one
PUCCH structure. Also this does not make sense to me. The problem was
that slot_ahead was 0, which logically cannot happen in this function
(because slot_ahead is illogical, we must give the radio some time). The
reason is that it uses if_inst->sl_ahead, which, prior to this commit,
was not set.

The init_nr_transport() function is called normally from main() through
init_eNB_afterRU(). In this case, we initialize if_inst->sl_ahead to
what is set in main(). In the PNF case, however, we call
init_nr_transport() from the PNF thread, when receiving the start
request. In the main(), we wait for this to happen, before setting
if_inst->sl_ahead. Hence, initializing this variable (which we should
safely be able to do) before solves the problem.

executables/nr-softmodem.c

@@ -690,6 +690,9 @@ int main( int argc, char **argv ) {
   nvIPC_Init(nrmac->nvipc_params_s);
 #endif
 
+  for (int idx = 0; idx < RC.nb_nr_L1_inst; idx++)
+    RC.gNB[idx]->if_inst->sl_ahead = sl_ahead;
+
   if (NFAPI_MODE==NFAPI_MODE_PNF) {
     wait_nfapi_init("main?");
   }
@@ -698,7 +701,6 @@ int main( int argc, char **argv ) {
     wait_RUs();
     // once all RUs are ready initialize the rest of the gNBs ((dependence on final RU parameters after configuration)
 
-    for (int idx=0;idx<RC.nb_nr_L1_inst;idx++) RC.gNB[idx]->if_inst->sl_ahead = sl_ahead;
     if (IS_SOFTMODEM_DOSCOPE || IS_SOFTMODEM_IMSCOPE_ENABLED) {
       sleep(1);
       scopeParms_t p;