netfilter: nf_conntrack_bridge: Fix memory leak when error

It should be added kfree_skb_list() when err is not equal to zero
in nf_br_ip_fragment().

v2: keep this aligned with IPv6.
v3: modify iter.frag_list to iter.frag.

Fixes: 3c171f49 ("netfilter: bridge: add connection tracking system")
Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/bridge/netfilter/nf_conntrack_bridge.c

@@ -88,6 +88,12 @@ static int nf_br_ip_fragment(struct net *net, struct sock *sk,
 
 			skb = ip_fraglist_next(&iter);
 		}
+
+		if (!err)
+			return 0;
+
+		kfree_skb_list(iter.frag);
+
 		return err;
 	}
 slow_path: