Fix backport of "tcp: detect malicious patterns in tcp_collapse_ofo_queue()"

Based on review from Eric Dumazet, my backport of commit
3d4bf93ac12003f9b8e1e2de37fe27983deebdcf to older kernels was a bit
incorrect.  This patch fixes this.

Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>