This attribute identifies the Topology Region to which the node
belongs. Nodes will only exchange topological information with
connected nodes in the same region.
The default value of 0 indicates that no regionId has been assigned
to the module. A module using the default regionId belongs to the
same region as the first neighbour which stages with it using a non-
zero regionId. If another neighbour tries to stage using a different
non-zero regionId, the trunk will not be allowed to come up.
Changing the value of the regionId will NOT cause the node to
restart.