Changes

cosmetic: osmo_ss7: Rearrange some contents

* Create sections for Routing Key, AS Traffic Mode, ASP Protocol which
  have their own enum/struct and set of APIs acting upon them.
* Move osmo_ss7_asp_disconnect() to its ASP section (was in AS section).

Change-Id: I592db59e27fa7b401d1281921e38817772308c00