A string of octets containing one bit per VLAN for VLANs
with values of 0 through 1023 in the management domain
on this port.
If the VLAN represented by setting a bit to '1' in the
bitmap is a normal VLAN, it allows packets belonging to
this vlan on this Private VLAN trunk port.
If the bit corresponding to a VLAN is set to '1' and if
the corresponding VLAN is a normal VLAN, then the local
system is enabled to transmit and receive frames as
normal VLAN
If the bit corresponding to a VLAN is set to '0', and if
the corresponding VLAN is not configured as a secondary
VLAN, then the system is disabled from sending and receiving
frames on that VLAN via this Private VLAN trunk port.