> rpc: add test-only sendmsgtopeer rpc
>
> This rpc can be used when we want a node to send a message, but
> cannot use a python P2P object, for example for testing of low-level
> net transport behavior.
> test: add basic tests for sendmsgtopeer to rpc_net.py
> test: add functional test for deadlock situation
This is a backport of core#28287
Depends on D17138