make gsup ipa name configurable in osmo-sgsn.cfg

Add a 'gsup ipa-name' VTY command which overrides the default
IPA name used by the SGSN on the GSUP link towards the HLR.
This is required for GSUP routing in multi-SGSN networks.

The 'gsup ipa-name' option can only be set via the config file
because changing the IPA name at run-time conflicts with active
GSUP connections and routes configured in the HLR. The osmo-sgsn
program must be restarted if its IPA name needs to change.

Related: OS#3356

Change-Id: Ib2f65fed9f56b9718e8a9647e3f01dce69870c1f
3 files changed