This implements some useful functions to use negentropy from RelayPool,
but does not integrate them with the rest of the app.
No changelog for the negentropy support right now as it is not hooked up
to any user-facing feature
Changelog-Fixed: Fixed a race condition in the networking logic that could cause notes to get missed in certain rare scenarios
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
