gprs_ns2: convert gprs_ns2_cause_str into an static inline

Be consistent with other implementation of get_value_string() in
libosomocore.

Change-Id: Ic79757df8683e0461c04f7ef9279e4fe645eb821
diff --git a/include/osmocom/gprs/gprs_ns2.h b/include/osmocom/gprs/gprs_ns2.h
index 975ddcb..ffc2ad8 100644
--- a/include/osmocom/gprs/gprs_ns2.h
+++ b/include/osmocom/gprs/gprs_ns2.h
@@ -7,6 +7,7 @@
 #include <netinet/in.h>
 
 #include <osmocom/core/prim.h>
+#include <osmocom/gprs/protocol/gsm_08_16.h>
 
 struct osmo_sockaddr;
 struct osmo_sockaddr_str;
@@ -74,6 +75,12 @@
 	NS_ENDPOINT_CONFIRM_CHANGE,
 };
 
+extern const struct value_string gprs_ns2_cause_strs[];
+
+/*! Obtain a human-readable string for NS primitives */
+static inline const char *gprs_ns2_cause_str(enum ns_cause val)
+{ return get_value_string(gprs_ns2_cause_strs, val); }
+
 struct osmo_gprs_ns2_prim {
 	struct osmo_prim_hdr oph;
 
@@ -185,7 +192,6 @@
 		struct gprs_ns2_nse *nse,
 		const struct osmo_sockaddr *sockaddr);
 void gprs_ns2_start_alive_all_nsvcs(struct gprs_ns2_nse *nse);
-const char *gprs_ns2_cause_str(int cause);
 const char *gprs_ns2_ll_str(struct gprs_ns2_vc *nsvc);
 char *gprs_ns2_ll_str_buf(char *buf, size_t buf_len, struct gprs_ns2_vc *nsvc);
 char *gprs_ns2_ll_str_c(const void *ctx, struct gprs_ns2_vc *nsvc);