Broadcast proofs from the network layer

Summary:
Let's have the network layer do the network stuff, shall we?

Depends on D9747

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, Detetivepro1, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Detetivepro1

Differential Revision: https://reviews.bitcoinabc.org/D9751