Before this change, server/host shutdown closed sockets directly in
ServerConnection::stop(), which bypassed the normal disconnect flow.
As a result, clients could be dropped without receiving a proper
DisconnectPacket during stop/kill/world-close paths.
Also, WinsockNetLayer::Shutdown() could destroy synchronization objects
while host-side recv threads were still exiting, causing a crash in
RecvThreadProc (access violation on world close in host mode).