blobstore: adjust order in spdk_xattr

It will save the space of spdk_xattr when put uint16_t after
uint32_t

Change-Id: Ie0712d8c3b16d90fc354847509fd87e1ffd93916
Signed-off-by: Ziye Yang <optimistyzy@gmail.com>
Reviewed-on: https://review.gerrithub.io/419453
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>

lib/blob/blobstore.h

@@ -53,11 +53,10 @@
 #define SPDK_BLOB_BLOBID_HIGH_BIT (1ULL << 32)
 
 struct spdk_xattr {
-	/* TODO: reorder for best packing */
 	uint32_t	index;
+	uint16_t	value_len;
 	char		*name;
 	void		*value;
-	uint16_t	value_len;
 	TAILQ_ENTRY(spdk_xattr)	link;
 };