FuzzedSock only supports peeking at one byte at a time, which is not
fuzzer friendly when trying to receive long data.
Fix this by supporting peek data of arbitrary length instead of only one
byte.
In the process of doing so, refactor `ConsumeNetAddr()` to generate the
addresses from IPv4, IPv6, Tor, I2P and CJDNS networks in the same way -
by preparing some random stream and deserializing from it. Similar code
was already found in `RandAddr()`.
