[avalanche] Enforce cooldown request present in AvalancheResponse
It is important in order to ensure the health of the network that node are able to throttle the requests they get from peers. This makes sure the core mechanics respect these cooldown requests.
Depends on D2117
Test Plan: Added tests case.
Reviewers: #bitcoin_abc, jasonbcox, Fabien
Reviewed By: #bitcoin_abc, jasonbcox, Fabien
Subscribers: jasonbcox, Fabien, teamcity
Differential Revision: https://reviews.bitcoinabc.org/D2122