[avalanche] Reduce aggressivity when connecting to avalanche peers

Summary: This reduce the number of connection failure before we fall back to non- avalanche outbounds. It still remains biased.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D15879