Determines how this port behaves when presented
with a Spanning Tree Explorer frame. The value
'disabled(2)' indicates that the port will not
accept or send Spanning Tree Explorer packets; any
STE packets received will be silently discarded.
The value 'forced(3)' indicates the port will
always accept and propagate Spanning Tree Explorer
frames. This allows a manually configured
Spanning Tree for this class of packet to be
configured. Note that unlike transparent bridging
this is not catastrophic to the network if there
are loops. The value 'auto-span(1)' can only be
returned by a bridge that both implements the
Spanning Tree Protocol and has use of the protocol
enabled on this port. The behavior of the port for
Spanning Tree Explorer frames is determined by the
state of dot1dStpPortState. If the port is in the
'forwarding' state, the frame will be accepted or
propagated. Otherwise it will be silently
discarded.