msc: Remove oversimplified todo entry and add a comment

Add a comment of why we want to accept this connection anyway.
diff --git a/openbsc/src/libmsc/osmo_msc.c b/openbsc/src/libmsc/osmo_msc.c
index b4facff..604c100 100644
--- a/openbsc/src/libmsc/osmo_msc.c
+++ b/openbsc/src/libmsc/osmo_msc.c
@@ -48,7 +48,11 @@
 	gsm0408_new_conn(conn);
 	gsm0408_dispatch(conn, msg);
 
-	/* TODO: do better */
+	/*
+	 * If this is a silent call we want the channel to remain open as long as
+	 * possible and this is why we accept this connection regardless of any
+	 * pending transaction or ongoing operation.
+	 */
 	if (conn->silent_call)
 		return BSC_API_CONN_POL_ACCEPT;
 	if (conn->loc_operation || conn->sec_operation || conn->anch_operation)