Bug#36066725 Regular mgmd hangs when sending it a stop node for ndbmtd

Root cause is that the mutexes 'theMultiTransporterMutex' and
'clusterMgrThreadMutex' are taken in different order in the
two respective call chains:

1) ClusterMgr::threadMain() -> lock() -> NdbMutex_Lock(clusterMgrThreadMutex)
   - ::threadMain(), holding clusterMgrThreadMutex -> TransporterFacade::startConnecting()
     - TF::startConnecting -> lockMultiTransporters()  <<<< HANG while holding clusterMgrThreadMutex

2) TransporterRegistry::report_disconnect() -> lockMultiTransporters()
   - ::report_disconnect(), holding theMultiTransporterMutex, -> TransporterFacade::reportDisconnect()
     - TF::reportDisconnect -> ClusterMgr::reportDisconnected()
       - ClusterMgr::reportDisconnected() -> lock()
         - lock() -> NdbMutex_Lock(clusterMgrThreadMutex) <<<< Held by 1)

Patch change TransporterRegistry::report_disconnect() such that the
theMultiTransporterMutex is released before calling reportDisconnect(NodeId).

It should be sufficient to hold theMultiTransporterMutex while
::report_disconnect check if we are disconnecting a multiTransporter,
and if all its Trps are in DISCONNECTED state. When this
finished we have set up 'ready_to_disconnect' and can release
theMultiTransporterMutex before -> reportDisconnect()

Change-Id: I19be0d9d92184efb8f20a92aa7189b9b85f069bc

Author: Ole John Aske

storage/ndb/src/common/transporter/TransporterRegistry.cpp

@@ -2373,14 +2373,14 @@ void TransporterRegistry::report_disconnect(TransporterReceiveHandle &recvdata,
       remove_allTransporters(this_trp);
     }
   }  // End of multiTransporter DISCONNECT handling
+  unlockMultiTransporters();
 
   if (ready_to_disconnect)  //  5)
   {
     DEBUG_FPRINTF((stderr, "(%u) -> reportDisconnect(node_id=%u)\n",
                    localNodeId, node_id));
     recvdata.reportDisconnect(node_id, errnum);
   }
-  unlockMultiTransporters();
   DBUG_VOID_RETURN;
 }