[Fireeye] Fix field conflicts

[legoguy1000]

What does this PR do?

Fix dns.id & network.iana_number field mappings.

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

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How to test this PR locally

Related issues

• CLoses [fireeye] Conflicting network.iana_number and dns.id field definition #2872

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• Start Time: 2022-03-28T00:38:53.280+0000

• Duration: 23 min 8 sec

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