The set of ports that should transmit egress packets
for this VLAN as untagged. The default value of this
object for the default VLAN (dot1qVlanIndex = 1) is a string
of appropriate length including all ports. There is no
specified default for other VLANs. If a device agent cannot
support the set of ports being set, then it will reject the
set operation with an error. For example, a
manager might attempt to set more than one VLAN to be untagged
on egress where the device does not support this IEEE 802.1Q
option.