BUG/MINOR: config: server on-marked-* statement is ignored in default-server

Commits e0d1bfb ("[MINOR] Allow shutdown of sessions when a server
becomes unavailable") and eb2c24a ("MINOR: checks: add on-marked-up
option") mentionned that the directive was supported in default-server
but while it can be stated there, it's ignored because the config value
is not copied from the default server upon creation of a new server.
Moving the statement to the "server" lines works fine though. Thanks
to Baptiste Assmann for reporting and diagnosing this bug.

These features were introduced in 1.5-dev6 and 1.5-dev10 respectively,
so no backport is needed.