[avalanche] Don't ban peers sending us unsolicited avalanche messages

Summary: This doesn't make sense to ban a peer for sending a message when some local option is missing, as there is no way for that peer to know about that. Just do the same than for any other message and ignore it.

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D11363