[MINOR] config: improve error reporting in listen sections

[MINOR] config: improve error reporting in listen sections

Try not to immediately exit on non-fatal errors while parsing a
listen section, so that the user has a chance to get most of the
errors at once, which is quite convenient especially during config
checks with the -c argument.
(cherry picked from commit 9389379f608d0776988125e52cbac12a2a2ad165)