HO: Add function to count currently ongoing handovers to a given BTS

In order to keep processing power at BTS at a defined level, the handover
decision might want to limit maximum number of slots that require RACH
detection.

Change-Id: I8908e37fe0d8d2eda906cc6301ba0969b25a5575
diff --git a/include/osmocom/bsc/handover.h b/include/osmocom/bsc/handover.h
index 9e2ba1a..a9349ee 100644
--- a/include/osmocom/bsc/handover.h
+++ b/include/osmocom/bsc/handover.h
@@ -7,3 +7,5 @@
 int bsc_handover_start(struct gsm_lchan *old_lchan, struct gsm_bts *bts);
 void bsc_clear_handover(struct gsm_subscriber_connection *conn, int free_lchan);
 struct gsm_lchan *bsc_handover_pending(struct gsm_lchan *new_lchan);
+
+int bsc_ho_count(struct gsm_bts *bts, bool inter_cell);