A string of octets containing one bit per VLAN for
VLANS with VlanIndex values of 2048 through 4095. The
first octet corresponds to VLANs with VlanIndex values
of 2048 through 2055; the second octet to VLANs 2056
through 2063; 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 MST instance,
then the bit corresponding to that VLAN is set to '1'.
If the length of this string is less than 256 octets,
any 'missing' octets are assumed to contain the value
of zero.