limit max streams support

pytorch/cuda/cuda_stream_manager.cpp

-#include <cassert>
+#include <cuda_runtime.h>
 
 #include "cuda_stream_manager.h"
 
@@ -8,6 +8,11 @@ CudaStreamManager* getCudaStreamManager(const size_t num_expert) {
     if (!smgr) {
         smgr = new CudaStreamManager(num_expert);        
     }
-    assert(smgr->num_expert == num_expert);
     return smgr;
 }
+
+void CudaStreamManager::sync() {
+	for (size_t i=0; i<MAX_STREAMS; ++i) {
+		cudaStreamSynchronize(streams[i]);
+	}
+}