[filebeat][netflow] copy ipv6 addresses to ECS fields

[immon]

Describe the enhancement:

IPv6 addresses are not copied to destination.ip and source.ip fields. As a consequence visualizations for ipv6 netflows "do not work".

IPv4 addresses are correctly handled in convert.go#L190 and convert.go#L202.

A workaround at this moment is to modify netflow input like this:

  input:
    processors:
    - copy_fields:
      when:
        has_fields: ['netflow.destination_ipv6_address']
      fields:
        - from: netflow.destination_ipv6_address
          to: destination.ip
    - copy_fields:
      when:
        has_fields: ['netflow.source_ipv6_address']
      fields:
        - from: netflow.source_ipv6_address
          to: source.ip

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)