sgsn: change configuration to the new NS2

Change the whole vty configuration for NS to be more flexible
and support more setups. Old configurations are invalid.

For further information see:
https://osmocom.org/projects/libosmocore/wiki/Network_service_(NS)

Depends-on: If5bd6b86e130772e6c93d640b0c637985416136d (osmo-sgsn)
Change-Id: I37d010bc4ae553c30feb2ebd2be66d23b96bf42a
2 files changed