This allows for a “shared secret” to be entered for a network switch,
segmenting traffic so that multiple people could use the feature
simultaneously without accidentally entering into or interfering with
each other's networks.
Takes a string specified in the configuration file (using the
net_%02i_secret key) and hashes it through SHA3-256 to prepend to each
data packet. This hash is used to compare packets on reception and
allow or discard them.
