Fix arc_release() refcount

Update arc_release to use arc_buf_size().  This hunk was accidentally
dropped when porting compressed send/recv, 2aa34383b.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #8000

module/zfs/arc.c

@@ -6825,7 +6825,7 @@ arc_release(arc_buf_t *buf, void *tag)
 
 		mutex_exit(&buf->b_evict_lock);
 		(void) zfs_refcount_add_many(&arc_anon->arcs_size,
-		    HDR_GET_LSIZE(nhdr), buf);
+		    arc_buf_size(buf), buf);
 	} else {
 		mutex_exit(&buf->b_evict_lock);
 		ASSERT(zfs_refcount_count(&hdr->b_l1hdr.b_refcnt) == 1);