node: Track last block that received a blockTip notification

Also signal m_tip_block_cv when StopRPC is called, for
consistency with g_best_block_cv. This is handled in
StopRPC instead of OnRPCStopped() because the latter
is deleted in a later commit.

Co-authored-by: TheCharlatan <seb.kung@gmail.com>
Co-authored-by: Ryan Ofsky <ryan@ofsky.org>

src/init.cpp

@@ -284,7 +284,7 @@ void Shutdown(NodeContext& node)
 
     StopHTTPRPC();
     StopREST();
-    StopRPC();
+    StopRPC(&node);
     StopHTTPServer();
     for (const auto& client : node.chain_clients) {
         client->flush();