This field isn't required by a worker and it's certainly not used by a
worker to listen on that specific interface. It also isn't required to
be set consistently and its use in-tree limited to the old load-balancing
script.
There's a bif called packet_source() which on a worker will provide
information about the actually used packet source.
Relates to zeek/zeek#2877.
This change allows users to specify an epoch length of 0, which means
that the user manually has to finish the epochs. A new next_epoch
function is introduced to allow users to manually end epochs.
Addresses GH-348
