message: Add suggested rescanblockchain comments
  From
diff: @@ -3459,6 +3459,11 @@ UniValue rescanblockchain(const JSONRPCRequest& request)
  if (tip_height) {
  start_block = locked_chain->getBlockHash(start_height);
  + // If called with a stop_height, set the stop_height here to
  + // trigger a rescan to that height.
  + // If called without a stop height, leave stop_height as null here
  + // so rescan continues to the tip (even if the tip advances during
  + // rescan).
  if (stop_height) {
  stop_block = locked_chain->getBlockHash(*stop_height);
  }
  