Update firewall-known-issues.md

[shyambasnet1]

Our documentation only mentions NAT, but it actually refers to DNAT, which can be confusing for the customer.

[prmerger-automator]

@shyambasnet1 : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit a64343a:

✅ Validation status: passed

File	Status	Preview URL	Details
articles/firewall/firewall-known-issues.md	✅Succeeded

For more details, please refer to the build report.

[Copilot]

Pull Request Overview

This PR clarifies networking terminology in Azure Firewall documentation by replacing "NAT" with the more specific "DNAT" in a known issues entry, reducing potential customer confusion about the type of Network Address Translation being referenced.

• Updated terminology from "NAT" to "DNAT" in firewall known issues documentation

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[v-dirichards]

@varunkalyana

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team