Indicates whether a specified notification is enabled or not.
If a bit corresponding to a notification is set to 1, then
the specified notification can be generated.
newRoot -- the newRoot notification as defined in BRIDGE-MIB.
topologyChange -- the topologyChange notification as
defined in BRIDGE-MIB.
inconsistency -- the stpxInconsistencyUpdate notification.
rootInconsistency -- the stpxRootInconsistencyUpdate
notification.
loopInconsistency -- the stpxLoopInconsistencyUpdate
notification.