Check for log level in zabbix_log() macro instead of __zbx_zabbix_log() function.

In several places in our code the following pattern is used for logging.

if (SUCCEED == zabbix_check_log_level(LOG_LEVEL_DEBUG))
{
     zabbix_log(LOG_LEVEL_DEBUG, ...);
}

Functionally the check for log level before calling zabbix_log() is unnecessary as __zbx_zabbix_log() checks for that itself.

However this is done for performance considerations - to avoid adding __zbx_zabbix_log() frame to the stack.

A more generic and universal approach would be to move the check outside of __zbx_zabbix_log() into zabbix_log() macro.