Rename define for (struct fellow_busy).io size

Ref #16

src/fellow_cache.c

@@ -492,7 +492,8 @@ struct fellow_busy {
 	/* protected by fco mtx */
 	uint8_t				io_idx;
 	uint8_t				io_outstanding;
-	struct fellow_busy_io		io[FCO_MAX_REGIONS];
+#define FBO_NIO FCO_MAX_REGIONS
+	struct fellow_busy_io		io[FBO_NIO];
 
 	// for fellow_busy_setattr()
 	uint32_t			va_data_len;
@@ -596,10 +597,10 @@ fellow_busy_io_get(struct fellow_busy *fbo, struct fellow_busy_io *stk)
 
 	AN(stk);
 
-	for (u = 0; u < FCO_MAX_REGIONS; u++) {
+	for (u = 0; u < FBO_NIO; u++) {
 		fbio = &fbo->io[fbo->io_idx];
 		fbo->io_idx++;
-		fbo->io_idx %= FCO_MAX_REGIONS;
+		fbo->io_idx %= FBO_NIO;
 		if (fbio->magic == 0 && fbio->type == FBIO_INVAL) {
 			INIT_OBJ(fbio, FELLOW_BUSY_IO_MAGIC);
 			fbio->fbo = fbo;