Fix nr_srssim linking problems when building with E2 support

In this case, there are a number of linker errors:

    /usr/bin/ld: libL2_NR.a(rrc_gNB.c.o): in function `nr_rrc_transfer_protected_rrc_message':
    /home/richie/oai/openair2/RRC/NR/rrc_gNB.c:330:(.text+0x6f6): undefined reference to `signal_rrc_msg'

However, nr_srssim does not need RRC, while it is being linked in. Thus,
link without nr_rrc and L2. For the remaining two linker problems:

- provide a definition of NR_IF_Module_init() as in most other
  simulators
- move rrc_get_max_nr_csrs() to nr_common.c. It is already declared in
  the corresponding header, and itself does not have anything to do with
  RRC radio configuration, therefore it does not belong to
  nr_radio_config.c

CMakeLists.txt

@@ -2080,7 +2080,7 @@ add_executable(nr_srssim
   )
 
 target_link_libraries(nr_srssim PRIVATE
-  -Wl,--start-group UTIL SIMU PHY_COMMON PHY_NR_COMMON PHY_NR PHY_NR_UE SCHED_NR_LIB SCHED_NR_UE_LIB MAC_UE_NR MAC_NR_COMMON nr_rrc L2_NR -lz -Wl,--end-group
+  -Wl,--start-group UTIL SIMU PHY_COMMON PHY_NR_COMMON PHY_NR PHY_NR_UE SCHED_NR_LIB SCHED_NR_UE_LIB MAC_UE_NR MAC_NR_COMMON -lz -Wl,--end-group
   m pthread ITTI dl nr_ue_phy_meas physim_common
   )
 

common/utils/nr/nr_common.c

@@ -1447,6 +1447,31 @@ unsigned short get_N_b_srs(int c_srs, int b_srs) {
   return srs_bandwidth_config[c_srs][b_srs][1];
 }
 
+// TODO: Implement to b_SRS = 1 and b_SRS = 2
+long rrc_get_max_nr_csrs(const int max_rbs, const long b_SRS)
+{
+  if(b_SRS>0) {
+    LOG_E(NR_RRC,"rrc_get_max_nr_csrs(): Not implemented yet for b_SRS>0\n");
+    return 0; // This c_srs is always valid
+  }
+
+  const uint16_t m_SRS[64] = { 4, 8, 12, 16, 16, 20, 24, 24, 28, 32, 36, 40, 48, 48, 52, 56, 60, 64, 72, 72, 76, 80, 88,
+                               96, 96, 104, 112, 120, 120, 120, 128, 128, 128, 132, 136, 144, 144, 144, 144, 152, 160,
+                               160, 160, 168, 176, 184, 192, 192, 192, 192, 208, 216, 224, 240, 240, 240, 240, 256, 256,
+                               256, 264, 272, 272, 272 };
+
+  long c_srs = 0;
+  uint16_t m = 4;
+  for(int c = 1; c<64; c++) {
+    if(m_SRS[c]>m && m_SRS[c]<max_rbs) {
+      c_srs = c;
+      m = m_SRS[c];
+    }
+  }
+
+  return c_srs;
+}
+
 frequency_range_t get_freq_range_from_freq(uint64_t freq)
 {
   // 3GPP TS 38.101-1 Version 19.0.0 Table 5.1-1: Definition of frequency ranges

openair1/SIMULATION/NR_PHY/srssim.c

@@ -68,6 +68,8 @@ nrUE_params_t *get_nrUE_params(void)
 channel_desc_t *UE2gNB[MAX_MOBILES_PER_GNB][NUMBER_OF_gNB_MAX];
 configmodule_interface_t *uniqCfg = NULL;
 
+NR_IF_Module_t *NR_IF_Module_init(int Mod_id) { return (NULL); }
+
 void e1_bearer_context_setup(const e1ap_bearer_setup_req_t *req)
 {
   abort();

openair2/LAYER2/NR_MAC_gNB/nr_radio_config.c

@@ -652,31 +652,6 @@ static void set_dl_maxmimolayers(NR_PDSCH_ServingCellConfig_t *pdsch_servingcell
     *pdsch_servingcellconfig->ext1->maxMIMO_Layers = min(maxMIMO_layers, ue_supported_layers);
 }
 
-// TODO: Implement to b_SRS = 1 and b_SRS = 2
-long rrc_get_max_nr_csrs(const int max_rbs, const long b_SRS) {
-
-  if(b_SRS>0) {
-    LOG_E(NR_RRC,"rrc_get_max_nr_csrs(): Not implemented yet for b_SRS>0\n");
-    return 0; // This c_srs is always valid
-  }
-
-  const uint16_t m_SRS[64] = { 4, 8, 12, 16, 16, 20, 24, 24, 28, 32, 36, 40, 48, 48, 52, 56, 60, 64, 72, 72, 76, 80, 88,
-                               96, 96, 104, 112, 120, 120, 120, 128, 128, 128, 132, 136, 144, 144, 144, 144, 152, 160,
-                               160, 160, 168, 176, 184, 192, 192, 192, 192, 208, 216, 224, 240, 240, 240, 240, 256, 256,
-                               256, 264, 272, 272, 272 };
-
-  long c_srs = 0;
-  uint16_t m = 4;
-  for(int c = 1; c<64; c++) {
-    if(m_SRS[c]>m && m_SRS[c]<max_rbs) {
-      c_srs = c;
-      m = m_SRS[c];
-    }
-  }
-
-  return c_srs;
-}
-
 static struct NR_SRS_Resource__resourceType__periodic *configure_periodic_srs(const NR_ServingCellConfigCommon_t *scc,
                                                                               const int uid)
 {