don't spawn nc, open socket directly

Right now, this package spawns [`nc` a.k.a. netcat](https://ss64.com/osx/nc.html) to listen for `awdl0` traffic; This is a bit hacky, doing it from within Node via its [UDP socket API](https://nodejs.org/api/dgram.html#dgram_udp_datagram_sockets)/[TCP socket API](https://nodejs.org/api/net.html#net_class_net_socket) would be cleaner.

I'm not an expert, and I failed miserably at porting these working implementations:

- [`opendrop`, written in Python, does](https://github.com/seemoo-lab/opendrop/blob/a61a2f6d9e03ef9ee99917cea7fe0a436b9d9556/opendrop/zeroconf.py#L1755-L1811) [DNS-SD](http://www.dns-sd.org) + [mDNS](http://www.multicastdns.org) a.k.a. Zeroconf via `awdl0`.
- [ Yggdrasil, written in Go, does](https://github.com/yggdrasil-network/yggdrasil-go/blob/d160eccab00443187e2343c707c60f37c7fbcfde/src/multicast/multicast_darwin.go#L55-L56) something similar to DNS-SD via `awdl0`.