MINOR: listener: provide a function to process all of a bind_conf's arguments

MINOR: listener: provide a function to process all of a bind_conf's arguments

The "bind" parsing code was duplicated for the peers section and as a
result it wasn't kept updated, resulting in slightly different error
behavior (e.g. errors were not freed, warnings were emitted as alerts)
Let's first unify it into a new dedicated function that properly reports
and frees the error.