The value of the write-able portion of the Bridge
ID, i.e., the first two octets, out of which the
priority is the most significant 4 bits of the first
octet of the (8 octet long) Bridge ID. The other
(last) 6 octets of the Bridge ID are given by the
value of dot1dBaseBridgeAddress in the BRIDGE-MIB.
The value of this object should always be a multiple
of 4096.