properly receive BSSMAP Clear Complete and Iu Release Complete

When sending a BSSMAP Clear or Iu Release, do not immediately discard the conn,
but wait until a BSSMAP Clear Complete / Iu Release Complete has been received.

Hence we will no longer show in the log that an incoming Release/Clear Complete
belongs to an unknown subscriber, but will still be around to properly log the
release.

Related: OS#3122
Change-Id: Ie4c6aaba3866d6e5b98004e8870a215e8cf8ffc1
diff --git a/src/libmsc/osmo_msc.c b/src/libmsc/osmo_msc.c
index a5184b2..cc67a5a 100644
--- a/src/libmsc/osmo_msc.c
+++ b/src/libmsc/osmo_msc.c
@@ -283,6 +283,11 @@
 		osmo_fsm_inst_dispatch(conn->fi, SUBSCR_CONN_E_UNUSED, NULL);
 }
 
+bool msc_subscr_conn_used_by(struct gsm_subscriber_connection *conn, enum msc_subscr_conn_use token)
+{
+	return conn && (conn->use_tokens & (1 << token));
+}
+
 const struct value_string msc_subscr_conn_use_names[] = {
 	{MSC_CONN_USE_UNTRACKED,	"UNTRACKED"},
 	{MSC_CONN_USE_COMPL_L3,		"compl_l3"},