The value that all bridges use for MaxAge when this bridge is acting as the root.
Note that 802.1D-1990 specifies that the range for this parameter is related to the
value of zyxelMrstpBridgeHelloTime. The granularity of this timer is specified by
802.1D-1990 to be 1 second. An agent may return a badValue error if a set is attempted
to a value which is not a whole number of seconds.