gprs_ns2: refactor: ensure all enums have GPRS_NS2_

All public enum should have the prefix GPRS_NS2_.

API change which must be synchronized with osmo-pcu,
osmo-gbproxy, osmo-sgsn.

Change-Id: I548ff12f7277cbb7e1a630a3dc02b738ce89be72
diff --git a/src/gb/gprs_bssgp2.c b/src/gb/gprs_bssgp2.c
index 5a8d41f..0f519ad 100644
--- a/src/gb/gprs_bssgp2.c
+++ b/src/gb/gprs_bssgp2.c
@@ -52,7 +52,7 @@
 	nsp.nsei = nsei;
 	nsp.u.unitdata.link_selector = lsp;
 
-	osmo_prim_init(&nsp.oph, SAP_NS, PRIM_NS_UNIT_DATA, PRIM_OP_REQUEST, msg);
+	osmo_prim_init(&nsp.oph, SAP_NS, GPRS_NS2_PRIM_UNIT_DATA, PRIM_OP_REQUEST, msg);
 	rc = gprs_ns2_recv_prim(nsi, &nsp.oph);
 
 	return rc;