docs: evpn: Add new Linux VXLAN Dataplane section

[robinchrist]

Little docs PR for EVPN:

Add a section that explains how Single VXLAN Devices (SVD) work behind the scenes and how to add and configure them (only the VXLAN devices, not anything else). It also briefly explains Traditional VXLAN Devices.

[greptile-apps]

Greptile Summary

This PR adds a new "Linux (VXLAN) Dataplane" section to the EVPN docs, covering the history and mechanics of Traditional vs. Single VXLAN Devices, the external (VXLAN_F_COLLECT_METADATA) and vnifilter (VXLAN_F_VNIFILTER) flags, with links to the upstream kernel commits. It also fixes several trailing-whitespace issues and a backtick rendering bug in the existing SVD example.

Confidence Score: 5/5

Safe to merge — documentation-only change with no functional impact; only minor P2 style nits remain.

All previously raised issues (mismatched backticks, grammar, single-backtick code literals) have been addressed. The two remaining findings are trivial P2 style suggestions that do not affect correctness or rendering.

No files require special attention.

Important Files Changed

Filename	Overview
doc/user/evpn.rst	Adds a new 130-line "Linux (VXLAN) Dataplane" section explaining Traditional vs. Single VXLAN Devices, the external/vnifilter flags, and their kernel history; also fixes trailing whitespace and a backtick rendering issue in the existing SVD example. Minor grammar nit on line 67 ("UDP ports" → "UDP port") and a redundant :abbr: expansion on lines 78–79.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Create VXLAN device] --> B{Use 'external' flag?}
    B -- No --> C[Traditional VXLAN Device\none VNI per device]
    B -- Yes --> D{Use 'vnifilter' flag?}
    D -- No --> E[Single VXLAN Device\nreceives ALL VNIs on port\nonly ONE allowed per UDP port]
    D -- Yes --> F[Single VXLAN Device with filter\nmultiple SVDs allowed per port\nbridge vlan vni add per VNI]
    E --> G[bridge vlan add vid + tunnel_info id]
    F --> G

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Prompt To Fix All With AI

This is a comment left during a code review.
Path: doc/user/evpn.rst
Line: 67

Comment:
**Singular/plural mismatch: "UDP ports"**

"for a specific UDP **ports**" should be "for a specific UDP **port**" — "a specific" requires the singular form.

```suggestion
   - ``external`` flag (``VXLAN_F_COLLECT_METADATA``): Flag that allows a VXLAN device to receive traffic for *all* VNIs for a specific UDP port, makes the device a "Single VXLAN Device", without ``vnifilter`` flag only one ``external`` VXLAN Device can exist per port
```

How can I resolve this? If you propose a fix, please make it concise.

---

This is a comment left during a code review.
Path: doc/user/evpn.rst
Line: 78-79

Comment:
**Redundant expansion of ``:abbr:`` directive**

The `:abbr:` directive already surfaces the expansion "Multi-VNI VXLAN Interface" in parentheses when rendered, so the trailing clause `which stands for "Multi-VNI VXLAN Interface"` repeats that information unnecessarily.

```suggestion
A better name would perhaps be :abbr:`MVVI (Multi-VNI VXLAN Interface)`.
```

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (2): Last reviewed commit: "docs: evpn: Add new Linux VXLAN Dataplan..." | Re-trigger Greptile}

[robinchrist]

@greptileai

[riw777]

looks good--thanks for this!