gsup_client: allow passing a unit id to identify with HLR

Before, each GSUP client would contact the HLR with an identical unit id, i.e.
"SGSN-00-00-00-00-00-00", with the result that some messages were sucked off by
the wrong client.

Pass explicit unit name from each gsup client user, so that OsmoMSC is "MSC"
and OsmoSGSN is "SGSN". Hence the HLR can properly route the messages.

Todo: also set some values instead of the zeros.

Unrelated cosmetic change while editing the arguments: gsup_client_create()'s
definition's oap client config arg name mismatched the one used in the
declaration. Use oapc_config in both.

Change-Id: I0a60681ab4a4d73e26fe8f0637447db4b6fe6eb2
4 files changed