We create a loop by not setting trans->callref = 0 before calling
trans_free(), as the latter would again send a MNCC_REL_IND up
the stack.
Also: Fix memory leak in case we try to read from mncc_sock
but socket is just gone.
This adds mncc_sock_from_cc() as a handler function for CC messages
to be passed to the MNCC interface. If there is no MNCC socket
registered, we immediately release any CC related messages.
Together with flushing all established CC transaction at MNCC socket
close time, this ensures that all resources are released and no
new resources can be established until the MNCC applicaiton has
re-attached.
Using this code we will soon be able to use LCR or other MNCC
applications via a unix domain socket.
The code is not actually used yet after this patch.