This optional parameter is used to alter the format of the
accounting log file from the standard radius format when
AcctLogFileFormatHook is not defined. AcctLogFileFormat is a string
containing special formatting characters. It specifies the format for each
line to be printed to the accounting log file. A newline will be
automatically appended. It is most useful if you use the %{attribute}
style of formatting characters (to print the value of the attributes in
the current packet).
