This seems kinda odd that `iter_module_map` is actually resetting the log levels all the time. Right not there's only one caller of `iter_crate_map`, but it seems weird to restrict this to only being used to resetting logging levels.

I'd be ok with yielding `*mod_entry` to the closure given (the value of `cur`) and then the caller can decide what it wants to do (it's got both the name and the logging level).

Also, I'd be ok with renaming `state` to `log_level` to reflect what it appears to actually be doing.