The version of Spanning Tree Protocol the bridge is
currently running. The value 'stpCompatible(0)'
indicates the Spanning Tree Protocol specified in
IEEE 802.1D and 'rstp/mstp(2)' indicates the Rapid
Spanning Tree Protocol specified in IEEE 802.1w and
Multiple Spanning Tree Protocol specified in IEEE
802.1s. New value may be defined as future versions
of the protocol become available.