NSR: Switchover with low hold timers

This feature includes support for 8000 BGP sessions with variable hold timers as low as 3 seconds for nonstop active routing (NSR) switchovers. You can configure up to 400 highly sensitive BGP sessions with hold timers of 10 seconds or lower, with the remaining sessions configured at either the default hold time of 90 seconds or a sparse distribution of hold timers in the range of 30 seconds and higher.