[ECS] nginx.access.remote_ip should map to source.address

[EthanStrider]

Currently, nginx.access.remote_ip does not map to source.address

apache2.access.remote_ip    ----->     source.address
iis.access.remote_ip        ----->     source.address
iis.error.remote_ip         ----->     source.address
traefik.access.remote_ip    ----->     source.address
nginx.access.remote_ip      --/-->     source.address

Source: https://www.elastic.co/guide/en/beats/libbeat/7.0/breaking-changes-7.0.html

For consistency sake, it probably should.