multiplexed_socket: avoid deadlock on cbMtx_

cbMtx_ is locked when onStateChangeCb_ is called. And onTlsStateChange
can call shutdown() which MUST NOT relock cbMtx_.

Change-Id: Ice8265b9a70f920a4f04451c19a752f260ef71b7

src/jamidht/multiplexed_socket.cpp

@@ -52,6 +52,7 @@ public:
 
     ~Impl() {
         if (!isShutdown_) {
+            if (endpoint) endpoint->setOnStateChange({});
             shutdown();
         } else {
             std::lock_guard<std::mutex> lkSockets(socketsMutex);
@@ -68,7 +69,6 @@ public:
         isShutdown_ = true;
         if (onShutdown_) onShutdown_();
         if (endpoint) {
-            endpoint->setOnStateChange({});
             std::unique_lock<std::mutex> lk(writeMtx);
             endpoint->shutdown();
         }