[avalanche] Deduplicate the log message when an avapoll is received

Summary: Upon receipt of an avapoll message, the message is logged by the net log and also the avalanche log which makes the latter one super verbose for no added value.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11949