The state of the port with respect to the SpanGuard feature.
true(1) - this port is being held in the blocking state by
the SpanGuard feature.
false(2) - this port is not being held in the blocking state
by the SpanGuard feature.
When this object has a value of true(1) setting its value
to false(2) will cause the SpanGuard feature to no longer
hold the port in the blocking state.
All other set operations on this object are undefined and
MUST NOT have any affect.