Fix Darwin multicast loopback by binding to INADDR_ANY

[jamesarich]

Summary

AsyncUDP::listenMulticast() bound the UDP socket to the multicast group address (224.0.0.69:port). Linux loops those datagrams back to sibling processes on the same host, but Darwin/BSD does not — so two meshtasticd native nodes on one macOS host never exchanged NodeInfo over UDP multicast.

Bind to INADDR_ANY:port on __APPLE__ instead. The uv_udp_set_membership() group join above still filters received traffic to the group. Linux is unchanged (still binds the group address, preserving the existing SO_BROADCAST receive-fanout behavior).

#if defined(__APPLE__)
    uv_ip4_addr("0.0.0.0", port, (struct sockaddr_in *)&uvAddr);
#endif
    if (uv_udp_bind(&_socket, (const struct sockaddr *)&uvAddr, 0) < 0) {

Test plan

• Rebuilt native-macos (meshtastic/firmware) with -DHAS_UDP_MULTICAST=1 and confirmed two native nodes now mesh over 224.0.0.69:4403 — both node DBs cross-populate.
• Linux meshing remains green: verified two nodes in the official meshtasticd Docker image cross-populate and deliver a text message.

[Copilot]

Pull request overview

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Adjusts UDP multicast listening on macOS/Darwin so multiple native nodes on the same host can receive looped-back multicast by binding to INADDR_ANY instead of the multicast group address.

Changes:

• Add an Apple-specific bind target override to 0.0.0.0:port in AsyncUDP::listenMulticast().
• Document the cross-platform rationale (Linux vs. Darwin/BSD behavior) in code comments.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.