avoid intermediate allocation in relayAddrs
avoid intermediate allocation in relayAddrs

now that we have the lock for the duration of the method, we don't need the intermediate
relays array. This removes it, and also extends the pre-allocation of the result array
by 2 so that it can cover two localhost and two private address bindings.

libp2p/go-libp2p,ipfs/go-libp2p,libp2p/go-libp2p