Enable multicast output

[sphaero]

It is already builtin we need to expose it

[sphaero]

simple czmq output test:

#include "czmq.h"

int main() {
    // mimick natnet actor
    zsock_t *data_socket = zsock_new(ZMQ_DGRAM);
    assert(data_socket);
    //int rc = zsock_connect(data_socket, "udp://239.0.0.1:5555");
    int rc = zsock_bind(data_socket, "udp://239.0.0.1:5555");
    assert(rc == 0);
    int i = 0;
    while (i<10)
    {
        zstr_sendm(data_socket, "239.0.0.1:5555");
        zstr_send(data_socket, "hello");
        zsys_warning("hello %i", i);
        i++;
        zclock_sleep(1000);
    }
    zsock_destroy(&data_socket);
    return 0;
}

[sphaero]

receive through socat (tested on OSX):

socat UDP4-RECVFROM:5555,ip-add-membership=239.0.0.1:0.0.0.0,fork - |cat

[sphaero]

It just works on Linux. Tested sending from linux(gazebosc) to linux(socat) and from linux(gazebosc) to osx(socat)

[sphaero]

recv does not work although there's no reason not to

[sphaero]

packet loss on wifi is huge. Over 50%

https://networkengineering.stackexchange.com/questions/36450/can-i-truly-multicast-over-wifi

[sphaero]

enabled igmp snooping and disabled wifi legacy rates, it's better now

[sphaero]

Some related bug in libzmq: zeromq/libzmq#4434

[sphaero]

Bug in libzmq is fixed. So this might help us! Wait for new build