Changes

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