libgb: Use library SS_L_NS instead lf local SS_NS

which removes some further dependencies of libgb to openbsc internal
code and data.
diff --git a/openbsc/src/gprs/gb_proxy.c b/openbsc/src/gprs/gb_proxy.c
index 518382d..87cfa61 100644
--- a/openbsc/src/gprs/gb_proxy.c
+++ b/openbsc/src/gprs/gb_proxy.c
@@ -596,7 +596,7 @@
 	struct gprs_nsvc *nsvc = nssd->nsvc;
 	struct gbprox_peer *peer;
 
-	if (subsys != SS_NS)
+	if (subsys != SS_L_NS)
 		return 0;
 
 	if (signal == S_NS_RESET && nsvc->nsei == gbcfg.nsip_sgsn_nsei) {
diff --git a/openbsc/src/gprs/gb_proxy_main.c b/openbsc/src/gprs/gb_proxy_main.c
index 5791dab..b853fbf 100644
--- a/openbsc/src/gprs/gb_proxy_main.c
+++ b/openbsc/src/gprs/gb_proxy_main.c
@@ -236,7 +236,7 @@
 	}
 	gbcfg.nsi = bssgp_nsi;
 	gprs_ns_vty_init(bssgp_nsi);
-	osmo_signal_register_handler(SS_NS, &gbprox_signal, NULL);
+	osmo_signal_register_handler(SS_L_NS, &gbprox_signal, NULL);
 
 	rc = gbproxy_parse_config(config_file, &gbcfg);
 	if (rc < 0) {
diff --git a/openbsc/src/gprs/sgsn_main.c b/openbsc/src/gprs/sgsn_main.c
index 640388d..9600c23 100644
--- a/openbsc/src/gprs/sgsn_main.c
+++ b/openbsc/src/gprs/sgsn_main.c
@@ -239,7 +239,7 @@
 	gprs_bssgp_vty_init();
 	gprs_llc_vty_init();
 	gprs_sndcp_vty_init();
-	/* FIXME: register signal handler for SS_NS */
+	/* FIXME: register signal handler for SS_L_NS */
 
 	rc = sgsn_parse_config(sgsn_inst.config_file, &sgsn_inst.cfg);
 	if (rc < 0) {