Also flip some callback asserts, because they can be reached by fuzzing
eventually.
Also update the bootstrapd checksum, since the alpine image changed a
bit.
If the `recvbuf` network function returns 0 all the time, that means
there is never any data available on the TCP socket. This change makes
it so there is a random amount of data available on the TCP socket.
This invalidates the bootstrap fuzzer corpus.
It can't happen in almost every reality, except when the RNG is fairly
broken and doesn't add 2 fake DHT friends on startup. Still, this code
should be defensive and never index outside `num_friends` elements.
Ideally this would be able to reach some of the events, so we can write
code to respond to those events, but so far only the friend request
event actually happens.
These help creating fuzzer fixtures with non-trivially constructed
objects and takes care of cleaning them up afterwards so the fuzzer code
can focus on the system under test.
