Add multicast UDP sockets

[danielinux]

No description provided.

[Copilot]

Pull request overview

Adds optional IPv4 UDP multicast support to wolfIP (gated by IP_MULTICAST), including IGMPv3 ASM membership reports and BSD-style multicast socket options, plus unit/interop tests and build targets.

Changes:

• Implement IGMPv3 membership report send/receive and multicast membership tracking for UDP sockets.
• Add multicast-related setsockopt/getsockopt options (*_ADD/DROP_MEMBERSHIP, *_MULTICAST_{IF,TTL,LOOP}) and multicast MAC/TTL/loop handling.
• Add unit tests, a Linux TAP interop smoke test, and document/build support for multicast.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
wolfip.h	Adds multicast socket option constants and mreq structs under IP_MULTICAST.
src/wolfip.c	Core multicast implementation (IGMP, membership tracking, UDP send/recv updates).
src/test/unit/unit_tests_multicast.c	New unit tests covering join/drop, receive gating, loopback send, IGMP query refresh.
src/test/unit/unit.c	Registers multicast unit tests when IP_MULTICAST is enabled.
src/test/test_multicast_interop.c	New Linux TAP interop test for multicast send/receive.
docs/API.md	Updates feature list to mention optional multicast UDP.
README.md	Documents multicast feature, options, and new test targets.
Makefile	Adds unit-multicast, interop build target, and multicast coverage targets.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #103

Scan targets checked: wolfip-bugs, wolfip-src

Findings: 2
2 finding(s) posted as inline comments (see file-level comments below)

This review was generated automatically by Fenrir. Findings are non-blocking.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

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