This object controls operation of the spanning tree
protocol (as distinguished from transparent bridging).
If set to stEnabled(1) then the spanning tree protocol
is enabled, subject to bridging constraints. If
noStFilterBpdu(2), then spanning tree is not active,
and Bridge PDUs received are discarded.
If noStPassBpdu(3) then spanning tree is not active
and Bridge PDUs are transparently forwarded. Note that
a device need not implement all of these options,
but that noStFilterBpdu(2) is required.