add mgcp_conn_rtp_type_names[]

First use in upcoming Ib89a6779e1d68c6600f00699d4303f6c0ee07132

Change-Id: If3d8bc68a3b26d3aa0ba7eedeab67b820889ed54
diff --git a/include/osmocom/mgcp/mgcp_conn.h b/include/osmocom/mgcp/mgcp_conn.h
index 7ac40ab..4f7b705 100644
--- a/include/osmocom/mgcp/mgcp_conn.h
+++ b/include/osmocom/mgcp/mgcp_conn.h
@@ -49,6 +49,11 @@
 	MGCP_RTP_OSMUX,
 	MGCP_RTP_IUUP,
 };
+extern const struct value_string mgcp_conn_rtp_type_names[];
+static inline const char *mgcp_conn_rtp_type_name(enum mgcp_conn_rtp_type val)
+{
+	return get_value_string(mgcp_conn_rtp_type_names, val);
+}
 
 /*! Connection type, specifies which member of the union "u" in mgcp_conn
  *  contains a useful connection description (currently only RTP) */