IF module slot_indication: send message in PNF

Use this function to implement distinct behavior for monolithic or PNF:

- monolithic: run the scheduler, as normal
- PNF: send a slot indication; the VNF will send an answer which the PNF
  will handle elsewhere.

Add function declarations to make nr_ulsim compile, as NR_IF_Module.c is
part of the MAC sources. As of now, this is necessary; I think the right
way would be to take NR_IF_Module.c out of the MAC, and make this a
"glue" library that sticks L1 and L2 together, in monolithic (in VNF, in
that case, we should not link in L1, and for the PNF not the L2,
creating separate executables... Rome was not built in one day).

openair2/NR_PHY_INTERFACE/NR_IF_Module.c

@@ -396,7 +396,15 @@ static void match_crc_rx_pdu(nfapi_nr_rx_data_indication_t *rx_ind, nfapi_nr_crc
   }
 }
 
-static void run_scheduler(module_id_t module_id, int CC_id, int frame, int slot)
+extern void handle_nr_slot_ind(uint16_t sfn, uint16_t slot);
+static void pnf_send_slot_ind(module_id_t module_id, int CC_id, int frame, int slot)
+{
+  (void)module_id;
+  (void)CC_id;
+  handle_nr_slot_ind(frame, slot);
+}
+
+static void run_scheduler_monolithic(module_id_t module_id, int CC_id, int frame, int slot)
 {
   NR_IF_Module_t *ifi = nr_if_inst[module_id];
 
@@ -509,7 +517,12 @@ NR_IF_Module_t *NR_IF_Module_init(int Mod_id) {
 
     nr_if_inst[Mod_id]->CC_mask=0;
     nr_if_inst[Mod_id]->NR_UL_indication = NR_UL_indication;
-    nr_if_inst[Mod_id]->NR_slot_indication = run_scheduler;
+    if (NFAPI_MODE == NFAPI_MONOLITHIC)
+      nr_if_inst[Mod_id]->NR_slot_indication = run_scheduler_monolithic;
+    else if (NFAPI_MODE == NFAPI_MODE_PNF)
+      nr_if_inst[Mod_id]->NR_slot_indication = pnf_send_slot_ind;
+    else // NFAPI_MODE_VNF
+      NULL;
     AssertFatal(pthread_mutex_init(&nr_if_inst[Mod_id]->if_mutex,NULL)==0,
                 "allocation of nr_if_inst[%d]->if_mutex fails\n",Mod_id);
   }