netfilter: nf_tables: fix *leak* when expr clone fail

When nft_expr_clone failed, a series of problems will happen:

1. module refcnt will leak, we call __module_get at the beginning but
   we forget to put it back if ops->clone returns fail
2. memory will be leaked, if clone fail, we just return NULL and forget
   to free the alloced element
3. set->nelems will become incorrect when set->size is specified. If
   clone fail, we should decrease the set->nelems

Now this patch fixes these problems. And fortunately, clone fail will
only happen on counter expression when memory is exhausted.

Fixes: 086f332167d6 ("netfilter: nf_tables: add clone interface to expression operations")
Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/nft_set_rbtree.c b/net/netfilter/nft_set_rbtree.c
index 38b5bda..36493a7 100644
--- a/net/netfilter/nft_set_rbtree.c
+++ b/net/netfilter/nft_set_rbtree.c
@@ -266,7 +266,7 @@
 	while ((node = priv->root.rb_node) != NULL) {
 		rb_erase(node, &priv->root);
 		rbe = rb_entry(node, struct nft_rbtree_elem, node);
-		nft_set_elem_destroy(set, rbe);
+		nft_set_elem_destroy(set, rbe, true);
 	}
 }