Diego Fronza authored Dec 18, 2020 and Matthijs Mekking committed Jan 29, 2021

This commit allows to specify "disabled" or "off" in
stale-answer-client-timeout statement. The logic to support this
behavior will be added in the subsequent commits.

This commit also ensures an upper bound to stale-answer-client-timeout
which equals to one second less than 'resolver-query-timeout'.

(cherry picked from commit 0ad6f594)