Changes

old-tags-against-master: ignore last osmo-bsc tags

This script tests if the last 3 tags of various Osmocom programs build
with current master libraries. Mark the last 3 OsmoBSC releases as known
failures, because of the unavoidable API break in libosmo-sigtran so the
job does not fail anymore.

Mark as known error:

  bsc_ctrl.c:639:18: error: invalid use of undefined type 'struct osmo_ss7_route'
    639 |         return rt->dest.as;

Related: OS#6617
Change-Id: Iac7e6ea7815dd2c3eb9c2636c0caa661161654ed