rsl: Rename the reason to release_mode and use the enum value

The API with 0 and 1 as legal values is hard to understand. Use the
recently introduced enum values instead.
diff --git a/openbsc/include/openbsc/abis_rsl.h b/openbsc/include/openbsc/abis_rsl.h
index f7e2e2a..c34492e 100644
--- a/openbsc/include/openbsc/abis_rsl.h
+++ b/openbsc/include/openbsc/abis_rsl.h
@@ -67,7 +67,8 @@
 int abis_rsl_rcvmsg(struct msgb *msg);
 
 uint64_t str_to_imsi(const char *imsi_str);
-int rsl_release_request(struct gsm_lchan *lchan, uint8_t link_id, uint8_t reason);
+int rsl_release_request(struct gsm_lchan *lchan, uint8_t link_id,
+			enum rsl_rel_mode release_mode);
 
 int rsl_lchan_set_state(struct gsm_lchan *lchan, int);
 
diff --git a/openbsc/include/openbsc/chan_alloc.h b/openbsc/include/openbsc/chan_alloc.h
index f1c890e..f2d3c78 100644
--- a/openbsc/include/openbsc/chan_alloc.h
+++ b/openbsc/include/openbsc/chan_alloc.h
@@ -46,7 +46,7 @@
 void lchan_reset(struct gsm_lchan *lchan);
 
 /* Release the given lchan */
-int lchan_release(struct gsm_lchan *lchan, int sacch_deact, int release_mode);
+int lchan_release(struct gsm_lchan *lchan, int sacch_deact, enum rsl_rel_mode release_mode);
 
 struct load_counter {
 	unsigned int total;
diff --git a/openbsc/include/openbsc/gsm_data_shared.h b/openbsc/include/openbsc/gsm_data_shared.h
index fda3b09..f81280f 100644
--- a/openbsc/include/openbsc/gsm_data_shared.h
+++ b/openbsc/include/openbsc/gsm_data_shared.h
@@ -196,8 +196,8 @@
 	uint8_t sapis[8];
 	int sacch_deact;
 
-	/** GSM 08.58 9.3.20 */
-	int release_mode;
+	/* Release handling */
+	enum rsl_rel_mode release_mode;
 
 	struct {
 		uint32_t bound_ip;