HO: move penalty timers to own file as proper API

Separate penalty timers API from specific struct members and move to own .h/.c
file, so that future code may re-use the API arbitrarily.

Change-Id: Ife975a1c7c17a500b1693be620475a8bea72f86f
diff --git a/include/osmocom/bsc/gsm_data.h b/include/osmocom/bsc/gsm_data.h
index 3da4fff..b8f8f81 100644
--- a/include/osmocom/bsc/gsm_data.h
+++ b/include/osmocom/bsc/gsm_data.h
@@ -79,13 +79,6 @@
 	uint8_t classmark3[14]; /* if cm3 gets extended by spec, it will be truncated */
 };
 
-/* penalty timers for handover */
-struct ho_penalty_timer {
-	struct llist_head entry;
-	uint8_t bts;
-	time_t timeout;
-};
-
 /* active radio connection of a mobile subscriber */
 struct gsm_subscriber_connection {
 	/* global linked list of subscriber_connections */
@@ -117,8 +110,7 @@
 	struct llist_head ho_dtap_cache;
 	unsigned int ho_dtap_cache_len;
 
-	/* penalty timers for handover */
-	struct llist_head ho_penalty_timers;
+	struct penalty_timers *ho_penalty_timers;
 };