gbproxy: update sns configuration to use ip-sns-bind
With libosmocore commit the SNS configuration requires a ip-sns-bind vty configuration
to define the binds which should be use.
Related: SYS#5354
Depends-on: I9ab8092bf286e7d90e92f5702a5404425e959c84 (libosmocore)
Change-Id: I11541540468584fc17a18fa294da5c9813c28d64
