Fix "net: ipv4: do not handle duplicate fragments as overlapping"

ade44640 ("net: ipv4: do not handle duplicate fragments as
overlapping") was backported to many stable trees, but it had a problem
that was "accidentally" fixed by the upstream commit 0ff89efb ("ip:
fail fast on IP defrag errors")

This is the fixup for that problem as we do not want the larger patch in
the older stable trees.

Fixes: ade44640 ("net: ipv4: do not handle duplicate fragments as overlapping")
Reported-by: Ivan Babrou <ivan@cloudflare.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ipv4/ip_fragment.c

@@ -425,6 +425,7 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 	 * fragment.
 	 */
 
+	err = -EINVAL;
 	/* Find out where to put this fragment.  */
 	prev_tail = qp->q.fragments_tail;
 	if (!prev_tail)
@@ -501,7 +502,6 @@ static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 
 discard_qp:
 	inet_frag_kill(&qp->q);
-	err = -EINVAL;
 	__IP_INC_STATS(net, IPSTATS_MIB_REASM_OVERLAPS);
 err:
 	kfree_skb(skb);