This timestamp indicates the time that the
BGP session last transitioned in or out of the Established
state. The value is the timestamp in nanoseconds relative to
the Unix Epoch (Jan 1, 1970 00:00:00 UTC).
The BGP session uptime can be computed by clients as the
difference between this value and the current time in UTC
(assuming the session is in the ESTABLISHED state, per the
session-state leaf).