SMS: Add value_string for TS 04.11 CP and RP state

Change-Id: I1b2f6fc6f455b0ba2a5732c567a4867bca97c3b0
diff --git a/include/osmocom/gsm/gsm0411_smr.h b/include/osmocom/gsm/gsm0411_smr.h
index 28f43de..75102f8 100644
--- a/include/osmocom/gsm/gsm0411_smr.h
+++ b/include/osmocom/gsm/gsm0411_smr.h
@@ -45,4 +45,10 @@
 int gsm411_smr_recv(struct gsm411_smr_inst *inst, int msg_type,
 	struct msgb *msg);
 
+extern const struct value_string gsm411_rp_state_names[];
+
+static inline const char *gsm411_rp_state_name(enum gsm411_rp_state rp_state) {
+	return get_value_string(gsm411_rp_state_names, rp_state);
+}
+
 /*! @} */