SMS: Add value_string for TS 04.11 CP and RP state

Change-Id: I1b2f6fc6f455b0ba2a5732c567a4867bca97c3b0
diff --git a/include/osmocom/gsm/gsm0411_smc.h b/include/osmocom/gsm/gsm0411_smc.h
index 7dfaa15..d05c018 100644
--- a/include/osmocom/gsm/gsm0411_smc.h
+++ b/include/osmocom/gsm/gsm0411_smc.h
@@ -64,4 +64,9 @@
 int gsm411_smc_recv(struct gsm411_smc_inst *inst, int msg_type,
 	struct msgb *msg, int cp_msg_type);
 
+extern const struct value_string gsm411_cp_state_names[];
+
+static inline const char *gsm411_cp_state_name(enum gsm411_cp_state cp_state) {
+	return get_value_string(gsm411_cp_state_names, cp_state);
+}
 /*! @} */