libmsc/gsm_09_11.c: do not abuse LOG_TRANS() and early trans allocation

In case of network-originated SS/USSD session establishment, we
need to verify the received GSUP PROC_SS_REQ message and make
sure that all mandatory IEs are present.

There is no sensible need to allocate a new transaction before
doing all the checks, other than the ability to use LOG_TRANS().
This complicates the code, so let's avoid the early allocation.

Change-Id: I4e027b19e8065a39324a1647957cef4066b82ce7
2 files changed