Store call CRV in caller_data.call_reference and use call private to hold the
FreeTDM channel object.
Remove isdn_data->channels_{local,remote,outbound}_crv arrays.
Allow (and force) inbound call state transition DIALTONE -> DOWN for
incoming RELEASE COMPLETE messages in NT mode.
Dialtone in NT mode works, everything else needs more testing.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>