The version of the Spanning Tree Protocol implemented
for this instance. ieeeSTP represents standard STP of 802.1d 1998.
ieeeRSTP stands for Rapid STP. Multiple STP or
MSTP (802.1s) is only supported in flat
mode, using instance 0. If future versions of the
IEEE Spanning Tree Protocol are released that are
incompatible with the current version, a new value will
be defined.