ms: add optional param to specify fixed APN IP address assigned to a MS

this allows to specify a fixed APN address for each subscriber in the
HLR. If the param is not provided in the resources config, the default
allocation type is used, which is to dynamically allocate an IP in the
supported range.

Change-Id: Ie6fcd7987dc7bc62a686bee3a10c67e3dd813419
5 files changed