MINOR: global: Set default tune.maxrewrite value during global structure init

MINOR: global: Set default tune.maxrewrite value during global structure init

When the global structure is initialized, instead of setting tune.maxrewrite to
-1, its default value can be immediately set. This way, it is always defined
during the configuration validity check. Otherwise, the only way to have it at
this stage, it is to explicity set it in the global section.