C18 Forward Delay Time. The maximum time that a LE
Client will maintain an entry for a non-local MAC
address in its LE_ARP cache in the absence of a
verification of that relationship, as long as the
Topology Change flag C19 is true.
atmLecForwardDelayTime SHOULD BE less than atmLecAgingTime.
When it is not, atmLecAgingTime governs LE_ARP aging.
This time value is expressed in seconds.