mgcp_client_endpoint_fsm: on term, still let conns wait for DLCX OK

When the mgcp_client_endpoint_fsm terminates, do not directly pull each
conn FSM instance (mgcp_client_fsm) into oblivion as well. Those should
emit a DLCX and wait for the "OK" response before deallocating.

In programs using the mgcp client endpoint FSM (osmo-bsc, osmo-msc),
this gets rid of false LMGCP ERROR logging related to DLCX like this:

  Cannot find matching MGCP transaction for trans_id 71998

Related: SYS#5529
Change-Id: I8fbfec5533e9be9cc7ea550df1e6639a0a215973
1 file changed