A string of octets containing one bit per VLAN. The
first octet corresponds to VLANs with VlanIndex values
1 through 8; the second octet to VLANs 9 through
16 etc. The most significant bit of each octet
corresponds to the lowest VlanIndex value in that octet.
For each VLAN that is mapped to this MSTP instance,
the bit corresponding to that VLAN is set to '1'.
Empty (zero) most significant octes are not mandatory.