Add support for new datatype: bfloat16

src/common.h

@@ -213,6 +213,9 @@ static size_t wordSize(ncclDataType_t type) {
 #endif
       return 1;
     case ncclHalf:
+#if defined(__CUDA_BF16_TYPES_EXIST__)
+    case ncclBfloat16:
+#endif
     //case ncclFloat16:
       return 2;
     case ncclInt: