bcachefs: bump max_active on btree_interior_update_worker

WQ_UNBOUND with max_active 1 means ordered workqueue, but we don't
actually need or want ordered semantics - and probably want a higher
concurrency limit anyways.

Signed-off-by: Kent Overstreet <[e-mail]>

fs/bcachefs/btree_update_interior.c

···
 int bch2_fs_btree_interior_update_init(struct bch_fs *c)
 {
 	c->btree_interior_update_worker =
-		alloc_workqueue("btree_update", WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
+		alloc_workqueue("btree_update", WQ_UNBOUND|WQ_MEM_RECLAIM, 8);
 	if (!c->btree_interior_update_worker)
 		return -BCH_ERR_ENOMEM_btree_interior_update_worker_init;