Changes

library/gsup: improve GSUP_IE templates

* Turn template params into templates
* Use proper template restrictions
* Remove unnecessary valueof()s
* Improve formatting

Change-Id: I67cc555a54113dccb11d0cc05cee66f5c2d795fe

library/gsup: rework f_gen_{tr,ts}_ss_ies() and SS templates

* Add missing param restrictions to SS related templates.
* f_gen_{tr,ts}_ss_ies(): proper template param restrictions.
* f_gen_ts_ss_ies(): return a template, not a value.
* f_gen_ts_ss_ies(): append IEs using list index.
* f_gen_ts_ss_ies(): isvalue() -> istemplatekind()
                     to allow passing template lists.
* f_gen_tr_ss_ies(): istemplatekind() -> ispresent()
                     to allow passing template lists.
* f_gen_tr_ss_ies(): 'omit' -> '*' for optional params.

Change-Id: Ia611ffa3845d48c5553c70f10981aa029d00d873

library/gsup: add src/dst name IEs to all SS templates

This enables us to send/match OSMO_GSUP_{SOURCE,DESTINATION}_NAME
IEs (if needed) and brings consistency to all SS related templates.

This patch makes the following testcases pass [again]:

* TC_mt_ussd_for_unknown_subscr,
* TC_proc_ss_for_unknown_session.

At some point osmo-msc started including the Source Name IE in
OSMO_GSUP_MSGT_PROC_SS_ERROR messages, which we didn't expect.

Change-Id: I8d947313a99491d2e4790bc06db863fe09d8b5cf