MSTP update - 18: adding STP path verctor utities

Added #STP #path #vector #utilities in MSTP module. This introduces the STP path vector comparison routine, which is used while processing xSTP PDU s. This decides whether specific path vector is superior to other ones or not.

#802-1S #MSTP update 18 ...
[commit 8742177261b48f47f81a04176045267634979afa]