The native way for logging is now by syslog priority and not by
logfile id. In practice that means that there's a function -
mxs_log_message - that takes a syslog priority. The new logging
macros (MXS_ERROR and friends) call that directly and the old
ones as well after having the logfile id translated into the
equivalent priority.
What is enabled or not is still by logfile id and hence the
priority is internally translated into a logfile id when checking
whether something really should be logged or not.