Set FPM log level earlier during init

The log level will be ignored throughout log events in `fpm_unix_init_main`, until
the very end when `zlog_set_level` is finally called.

In particular, `fpm_unix_conf_wp` may throw notices like this:

> [08-Nov-2014 17:13:36] NOTICE: [pool www] 'user' directive is ignored when…

Which will still appear even if `log_level` in php-fpm.conf is set to `warning`+

To reproduce, set "log_level" in `php-fpm.conf` to warning. On startup as non-root, these two notices will still appear:

> [08-Nov-2014 17:13:36] NOTICE: [pool www] 'user' directive is ignored when FPM is not running as root
> [08-Nov-2014 17:13:36] NOTICE: [pool www] 'user' directive is ignored when FPM is not running as root

Adresses https://bugs.php.net/bug.php?id=68381