buddy: in struct i_wait, separate initiator and allocator owned members

In particular with uint8_t, we risk writes to be non atomic and
overwrite neighboring members

src/buddy.h

@@ -295,14 +295,16 @@ enum i_wait_state {
 
 struct i_wait {
 	unsigned			magic;
-#define I_WAIT_MAGIC		0x7f6303bc
-	uint8_t			alloced; // how many of n
-	uint8_t			finid;
-	uint8_t			next;
-	enum i_wait_state		state;
-	VTAILQ_ENTRY(buddy_reqs)	list;
-	pthread_mutex_t		wait_mtx;
+#define I_WAIT_MAGIC			0x7f6303bc
+	// owned by initiator
+	uint8_t				finid;
+	uint8_t				next;
+	pthread_mutex_t			wait_mtx;
 	pthread_cond_t			wait_cond;
+	VTAILQ_ENTRY(buddy_reqs)	list;
+	// updated under lock - KEEP SEPERATE FROM "owned by initiator"
+	uint8_t				alloced; // how many of n
+	enum i_wait_state		state;
 };
 
 #define BUDDY_REQS_AUDIT