Replace oai-spgwu-tiny by the new oai-upf

Change UE IP network address blocks for a 'Private-Use' range. Address block 12.1.0.0/16 is for public use, so we should not use it for the UEs (https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml)