gsup client: add up_down_cb(), add osmo_gsup_client_create3()

For the GSUP clients in upcoming D-GSM enabled osmo-hlr, it will be necessary
to trigger an event as soon as a GSUP client connection becomes ready for
communication. Add the osmo_gsup_client->up_down_cb.

Add osmo_gsup_client_create3() to pass the up_down_cb in the arguments. Also
add a cb data argument to populate the already existing osmo_gsup_client->data
item directly from osmo_gsup_client_create3().

We need the callbacks and data pointer in the osmo_gsup_client_create()
function right before startup, because this function immediately starts up the
connection. Who knows whether callbacks might trigger right away.

Because there are so many arguments, and to prevent the need for ever new
versions of this function, pass the arguments as an extendable struct.

Change-Id: I6f181e42b678465bc9945f192559dc57d2083c6d
2 files changed