[avalanche] Enforce cooldown request present in AvalancheResponse

Summary:
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