A string of octets containing one bit per VLAN. The
first octet corresponds to VLANs with VlanIndex values
of 0 through 7; the second octet to VLANs 8 through
15; etc. The most significant bit of each octet
corresponds to the lowest value VlanIndex in that octet.
For each VLAN, if it is mapped to this MISTP instance,
then the bit corresponding to that VLAN is set to '1'.