dht find connected peers

This PR extends the DHT to send information re: peer "connectedness".
This means that --upon resolving dht queries -- connected peers will
signal whether or not they are directly connected to the peer. this is
in preparation for mesh messaging, and our "STUN" for NAT traversal.
minor thing but you can use `iota` to enumerate
``` go
const (
  Not = iota
  Connected
  Can
  Cannot
)
```