gprs_ns2: add gprs_ns2_nse_nsei() to get the nsei of a nse

Change-Id: I5f67e6a9bf4cb322bd169061fee0a528012ed54d
diff --git a/src/gb/libosmogb.map b/src/gb/libosmogb.map
index 980b317..3d1d5d6 100644
--- a/src/gb/libosmogb.map
+++ b/src/gb/libosmogb.map
@@ -98,6 +98,7 @@
 gprs_ns2_ll_str_buf;
 gprs_ns2_ll_str_c;
 gprs_ns2_nse_by_nsei;
+gprs_ns2_nse_nsei;
 gprs_ns2_nsvc_by_nsvci;
 gprs_ns2_nsvc_by_sockaddr;
 gprs_ns2_recv_prim;