This attribute is indicative of the number of TB forwarding table entries
free. These entries could be used by static entries or by dynamic entries.
This counter wraps around its maximum value of 4294967295.
A consistently high value for this attribute indicates that there is a
resource surplus here, in terms of the memory requirements of the
forwarding table. This surplus could be utilized elsewhere if need be.
The value of this attributes directly influenced by the value of the
attribute tbFwdTableNumEntries.