An upper-bound on the time thate stale routes will be
retained by a router after a session is restarted. If an
End-of-RIB (EOR) marker is received prior to this timer
expiring stale-routes will be flushed upon its receipt - if
no EOR is received, then when this timer expires stale paths
will be purged. This timer is referred to as the
Selection_Deferral_Timer in RFC4724