Backport of trunk fix to 3.2
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commit 6ab2126364e9e58b4e7d738f4e15aceec8364119
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Thu Feb 28 20:29:40 2013 +0100

    First attempt at fixing infinite mapping

    When accessing baidu.com, it replies with the MP_CAPABLE option (because
    it seems to just echo back any unknown option to the sender). However,
    further baidu.com off course does not support MPTCP and will reply to
    our data-seq without a data-ack. This is an easy scenario to trigger a
    fallback to infinite through Section 3.6 of the RFC.

    This is a first attempt to contacting baidu.com work.

    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>

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Backport of trunk fix to 3.2
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commit 0b874ccbc43e971131e95524f8bedee9f4917c0f
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Fri Mar 1 12:50:09 2013 +0100

    Fix: Stop retransmitting third ack after fourth ack without data-ack

    RFC 6824 says that any fourth ack should stop the retransmission of the
    third ack with MP_JOIN.

    This patch fixes it, as previously we only stopped retransmitting if the
    fourth ack had a DATA_ACK.

    Reported-by: Varun Taneja <sunvarun@gmail.com>
    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
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Backport of trunk fix to 3.2
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commit 06012238ea826d8843e27e68e8bcab6fec2fa199
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Fri Mar 1 14:38:15 2013 +0100

    Fix further infinite mapping

    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>

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Backport of trunk fix to 3.2
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commit 9cb0863536a2b0b8717e18847baf5b2d3003eae8
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Fri Mar 1 17:26:21 2013 +0100

    Cleanup

    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>

--
pkts_acked is used in the tcp_ack function, but was not declared.