Invert broker format for StoreStream

Place the image metadata first so we can directly receive the
jf_assembler stream into this data structure.

jf-live-writer/include/broker_format.hpp

@@ -9,6 +9,8 @@ const static uint8_t OP_END = 2;
 #pragma pack(push)
 #pragma pack(1)
 struct StoreStream {
+    ImageMetadata image_metadata;
+
     int64_t run_id;
     uint32_t i_image;
     uint32_t n_images;
@@ -16,8 +18,6 @@ struct StoreStream {
     uint32_t image_x_size;
     uint32_t op_code;
     uint32_t bits_per_pixel;
-
-    ImageMetadata image_metadata;
 };
 #pragma pack(pop)
 #endif //SF_DAQ_BUFFER_BROKER_FORMAT_HPP