message: Avoid shutting down socket channels
  Closing one communication channel such as read or write may cause the
  remote side to abort the entire connection since it assumes an error or
  disconnect.
diff: @@ -184,7 +184,6 @@ void multiplexer::shutdown_reading(const socket_manager_ptr& mgr) {
  } else if (auto index = index_of(mgr); index != -1) {
  mgr->block_reads();
  auto& entry = pollset_[index];
  - std::ignore = shutdown_read(socket{entry.fd});
  entry.events &= ~input_mask;
  if (entry.events == 0)
  del(index);
  @@ -202,7 +201,6 @@ void multiplexer::shutdown_writing(const socket_manager_ptr& mgr) {
  } else if (auto index = index_of(mgr); index != -1) {
  mgr->block_writes();
  auto& entry = pollset_[index];
  - std::ignore = shutdown_write(socket{entry.fd});
  entry.events &= ~output_mask;
  if (entry.events == 0)
  del(index);
  