Don't exclusively bind the mDNS broadcast listen port

[brokeh]

I'd like to make use of the report-client-info setting to include my internal client hostnames in logs where my pfSense router is the DNS resolver for my network, however, enabling that option exclusively binds to port UDP/5353 for the mDNS listener which then breaks my Avahi mDNS forwarder which wants to bind to the same port.

This should be done by setting the SO_REUSEADDR option before binding to the socket. See https://linux.die.net/man/3/setsockopt#:~:text=a%20Boolean%20option.-,SO_REUSEADDR,-Specifies%20that%20the

I think the relevant place to set this would be the net.ListenMulticastUDP in

nextdns/discovery/mdns.go

Lines 78 to 85 in 1610583

	if conn, err = net.ListenMulticastUDP("udp4", &iface, ipv4Addr); err == nil {
	go r.read(ctx, conn)
	conns = append(conns, conn)
	}
	if conn, err = net.ListenMulticastUDP("udp6", &iface, ipv6Addr); err == nil {
	go r.read(ctx, conn)
	conns = append(conns, conn)
	}

but from what I can tell from the documentation it is not possible to set socket options when using this method.

[rs]

It does not seem to be easily doable with Go. I'm not sure it would work correctly anyway.