netflow: replace invalid field value

[efd6]

What does this PR do?

This replaces an invalid field value. A parallel change is required in x-pack/filebeat/input/netflow to bring that into line. This change is independent of that and will remain effective after that has been merged.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes netflow using invalid field values according to ECS #3047

Screenshots

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

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Build stats

• Start Time: 2022-04-14T04:06:03.874+0000

• Duration: 14 min 31 sec

Test stats 🧪

Test	Results
Failed	0
Passed	92
Skipped	0
Total	92

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