ca_ready_cb and cc_parallel_ready_cb called etcp_connection_close
synchronously on non-selected connections from within the ready_cbk
callback chain. This corrupts senders_list in topo_group, causing
UAF in topo_group_start_link_nat_check.
Now uses uasync_call_soon (zero-delay timer) to defer the close
to the next event loop iteration, after the callback chain completes
and callbacks_running flag is reset.
Evgeny
9378b18ce7