MNCC and MNCC_LCHAN_MODIFY (and ack/nack)

Hi Andreas, all, right now there is no ack/nack for the MNCC_LCHAN_MODIFY and I would like to introduce _ACK/_NACK for it. The MNCC_LCHAN_MODIFY message will end up calling the gsm0808_assignment_request of the BSC API and in case the call is not on a TCH it will assign a new TCH. Things will go wrong from here. osmo-nitb does not implement the assign_compl/assign_fail callbacks and in case of an assignment failure we crash right now (master has dummy callbacks). I would like to introduce MNCC_LCHAN_MODIFY_ACK/MNCC_LCHAN_MODIFY_NACK, change the mncc_sock.c:mncc_setup_ind and handling of MNCC_CALL_CONF_IND. what do you think? holger