To that end, since resolving `/dnsaddr` addresses needs
"fully qualified" multiaddresses when dialing, i.e. those
that end with the `/p2p/...` protocol, we make sure that
dialing always uses such fully qualified addresses by
appending the `/p2p` protocol as necessary. As a side-effect,
this adds support for dialing peers via "fully qualified"
addresses, as an alternative to using a `PeerId` together
with a `Multiaddr` with or without the `/p2p` protocol.