Add an OpenWrt package for udpspeeder-simd

Status: planned
Persona: Ingrid (OpenWrt feed maintainer)
Serves: https://github.com/openwrt/packages/issues/28562
Scope: the packages and udpspeeder-simd components
Package maintainer: David Connolly david@connol.ly
Target: OpenWrt master for the first pull request; a release-branch backport is constrained by policy (see the rules below)
Decisions: call/0004 (coexist, dynamic linking), call/0005 (build adjustments in the fork)

Why

The issue at https://github.com/openwrt/packages/issues/28562 asks for the performance-optimised UDPspeeder on low-end devices; the reporter's target is ath79/generic, a MIPS 24Kc core. UDPspeeder-simd is that optimised fork. Rather than repoint the existing net/udpspeeder package at a fork, this milestone adds a separate net/udpspeeder-simd package that coexists with udpspeeder.

On ath79 the gain comes from the portable word-width XOR and the portable Reed-Solomon speedups, not from SIMD. The source carries no MIPS SIMD path, and none is worthwhile on the 24Kc core (MSA is absent on that core, and its optional DSP ASE targets fixed-point math rather than vector XOR).

OpenWrt maintainer rules this milestone follows

From the feed's CONTRIBUTING.md (pinned in the packages worktree) and https://openwrt.org/docs/guide-developer/packages :

Pin the source to a fixed commit or tag with a PKG_MIRROR_HASH, never a branch head or a "latest" archive. This is also what the issue requests.
PKG_MAINTAINER is a real name and a real, public email (David Connolly david@connol.ly). A GitHub noreply address is rejected.
PKG_LICENSE is the SPDX identifier MIT, with PKG_LICENSE_FILES naming the license file (LICENSE.md) in the fork.
PKG_RELEASE starts at 1.
No dependencies outside the OpenWrt core packages or this feed.
Each pull-request commit subject is prefixed with the package name (udpspeeder-simd: add package) and carries a Signed-off-by that matches the author (a real name and a public email), with no automated co-author trailer (the packages rule in call/0003). The sign-off is the DCO, which is separate from the co-author trailer.
A test.sh beside the Makefile lets the OpenWrt CI runtime-test the package on its supported architectures.
Release branches (openwrt-XX.YY) take only security and bug fixes. Adding a new package to a release branch is against policy, so a backport is not a routine cherry-pick (see #backports).

Design decisions

Interop (call/0004): a distinct package udpspeeder-simd with distinct paths (/usr/bin/udpspeeder-simd, /etc/config/udpspeeder-simd, /etc/init.d/udpspeeder-simd), no file clash with udpspeeder, no CONFLICTS.
Linking (call/0004): dynamic, with DEPENDS on the shared libraries the binary needs, like the existing udpspeeder. No static build. A static C++ binary is larger on flash, which works against the low-end devices this issue targets, and static linking runs against OpenWrt's shared-library model.
Build adjustments (call/0005): they live in the fork's makefile, after which the .host-software pin is updated. The fork commits keep the normal sign-off and co-author trailer; only the packages repo drops the trailer. In practice no fork change was needed: the feed's cc_cross and gitversion Build/Prepare sufficed.
SDK for local validation: the public prebuilt x86_64 snapshot SDK (the one OpenWrt CI uses), not a from-source build (make world proved excessive for this). The embedded openwrt component stays but is not required for this path. Local validation covers x86_64; multi-architecture, including ath79/generic, runs in the CI lane. Snapshot OpenWrt packages are .apk, not .ipk.
CI validation (#ci-sdk-lane): lives in the host repo (.github/workflows/udpspeeder-simd-sdk.yml), never in the openwrt PR, so the PR stays a discrete package addition. It builds the fork's package branch against the current snapshot SDK for x86/64 and ath79/generic.
Release users (#backports): OpenWrt policy blocks a new package on release branches, so there is no backport. docs/udpspeeder-simd-on-openwrt-releases.md shows a developer or power user how to self-apply it with a release SDK or buildroot.