bsc_msc: Remove use_count from the subscriber connection

A channel will be released in case of
    * Errors via the clear_request callback...
    * no more transactions and operations are going on.

This means that if we do something without a transaction
the channel might be closed down right away. The bug fix
will be to create a transaction/operation.
diff --git a/openbsc/src/silent_call.c b/openbsc/src/silent_call.c
index 397a3e4..7ba451b 100644
--- a/openbsc/src/silent_call.c
+++ b/openbsc/src/silent_call.c
@@ -57,7 +57,6 @@
 		conn->silent_call = 1;
 		/* increment lchan reference count */
 		dispatch_signal(SS_SCALL, S_SCALL_SUCCESS, &sigdata);
-		use_subscr_con(conn);
 		break;
 	case GSM_PAGING_EXPIRED:
 		DEBUGP(DSMS, "expired\n");
@@ -135,7 +134,8 @@
 	if (!conn->silent_call)
 		return -EINVAL;
 
-	put_subscr_con(conn);
+	conn->silent_call = 0;
+	msc_release_connection(conn);
 
 	return 0;
 }