This is to avoid having two sendme.{c|h} in the repository since the subsystem
is implemented in src/core/or/sendme.{c|h}.
Fixes#30769
Signed-off-by: David Goulet <dgoulet@torproject.org>
This includes the link handshake variations for proposal220.
We'll use this for testing first, and then use it to extend our
current code to support prop220.