Make separate header for nr_pdcp instead of using 4G pdcp

Creates function that have nr_pdcp_ prepended to their name, and change
the signature of some functions for the 5G PDCP:

- nr_pdcp_layer_init()
- nr_pdcp_data_req()
- nr_pdcp_remove_UE()
- nr_pdcp_config_set_security()
- nr_pdcp_remove_UE()
- Make separate functions for nr_pdcp_data_req_srb/drb()

openair2/GNB_APP/gnb_app.c

@@ -49,7 +49,7 @@
 #include "f1ap_du_task.h"
 #include "nfapi/oai_integration/vendor_ext.h"
 #include <openair2/LAYER2/nr_pdcp/nr_pdcp.h>
-#include "openair2/LAYER2/PDCP_v10.1.0/pdcp.h"
+#include "openair2/LAYER2/nr_pdcp/nr_pdcp_oai_api.h"
 #include "openair2/E1AP/e1ap.h"
 #include "gnb_config.h"
 extern unsigned char NB_gNB_INST;