Add strings with PH primitive names

It's useful debugging helper while troubleshooting L1-related issues.

Change-Id: Id7a6d478fd725c51f54ad746bdf9b9095579ff77
Reviewed-on: https://gerrit.osmocom.org/117
Tested-by: Jenkins Builder
Reviewed-by: Max <msuraev@sysmocom.de>
Reviewed-by: Holger Freyther <holger@freyther.de>
diff --git a/include/osmocom/gsm/l1sap.h b/include/osmocom/gsm/l1sap.h
index 1af8ba8..ad942ea 100644
--- a/include/osmocom/gsm/l1sap.h
+++ b/include/osmocom/gsm/l1sap.h
@@ -14,6 +14,8 @@
 	PRIM_TCH_RTS,		/*!< \brief TCH */
 };
 
+extern const struct value_string osmo_ph_prim_names[];
+
 /*! \brief PH-SAP related primitives (L1<->L2 SAP) */
 enum osmo_mph_info_type {
 	PRIM_INFO_TIME,		/*!< \brief Current GSM time */