MSTP update - 4: added xSTP protocol constants and PDU defenitions

Added #xSTP #protocol #constant s and #PDU #definition s in MSTP module. Updated LIB module with #IEEE defined #xSTP #MAC #address es and #LLC #address constants. Added #STP and #MSTP PDU definitions in MSTP module.

#802-1S MSTP update 4 + #Lib update 10 ...
[commit d60cb9373aa02b4fd37192e490a86d8d1471766f]