EPGM couldn't receive message under pub-sub mode

[qdztxc]

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Issue description

In pub-sub mode, use EPGM in same machine.

Environment

• libzmq version (commit hash if unreleased): 4.3.6
• OS: debian12

Minimal test code / Steps to reproduce the issue

publisher:

#include <zmq.hpp>
#include <string>
#include <iostream>
#include <thread>
#include <chrono>

int main() {
    zmq::context_t context(1);

    zmq::socket_t publisher(context, zmq::socket_type::pub);
    std::string connection_string = "epgm://eno1;239.192.1.1:5555";
    
    try {
        publisher.bind(connection_string);
        std::cout << "Publisher bound to " << connection_string << std::endl;
    } catch (zmq::error_t& e) {
        std::cerr << "Failed to bind publisher: " << e.what() << std::endl;
        return 1;
    }

    int count = 0;
    while (true) {
        std::string message = "Message " + std::to_string(count++);
        zmq::message_t zmq_message(message.data(), message.size());
        
        try {
            publisher.send(zmq_message, zmq::send_flags::none);
            std::cout << "Sent: " << message << std::endl;
        } catch (zmq::error_t& e) {
            std::cerr << "Failed to send message: " << e.what() << std::endl;
        }

        std::this_thread::sleep_for(std::chrono::seconds(1));
    }

    return 0;
}

subscriber:

#include <zmq.hpp>
#include <string>
#include <iostream>

int main() {
    zmq::context_t context(1);

    zmq::socket_t subscriber(context, zmq::socket_type::sub);
    std::string connection_string = "epgm://eno1;239.192.1.1:5555";
    
    try {
        subscriber.connect(connection_string);
        std::cout << "Subscriber connected to " << connection_string << std::endl;

        subscriber.set(zmq::sockopt::subscribe, "");
    } catch (zmq::error_t& e) {
        std::cerr << "Failed to connect subscriber: " << e.what() << std::endl;
        return 1;
    }

    while (true) {
        zmq::message_t message;
        try {
            auto result = subscriber.recv(message, zmq::recv_flags::none);
            if (result) {
                std::string received_msg(static_cast<char*>(message.data()), message.size());
                std::cout << "Received: " << received_msg << std::endl;
            }
        } catch (zmq::error_t& e) {
            std::cerr << "Failed to receive message: " << e.what() << std::endl;
        }
    }

    return 0;
}

What's the actual result? (include assertion message & call stack if applicable)

subscriber couldn't receive any message.

What's the expected result?

subscriber should recieve message sent by publisher.