This commit makes the minimal amount of changes to switch us from
whyrusleeping/mdns to grandcat/zeroconf. Of note, rather than asking the
host.Host which addrs we're available to listen on, we push this to the
zeroconf library (which runs across available ifaces).

1. If we receive multiple ipv4 addresses, ensure that we convert them
all to multiaddrs and store them in the peerstore.
2. Ensure we don't allocate a new resolver on every tick. Instead reuse
this by storing it in our mdns type.
3. Attempt choosing a port.

Ideally, we'd dynamically announce ports based on the current interfaces.
However, we'd like to merge this ASAP.