Backport from trunk to 3.2

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commit 3d94a3b4895e2fcca5931c38fc062ef760421040
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Tue Feb 19 21:21:23 2013 +0100

    Fix mptcp_debug

    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Backport of trunk fix to 3.2

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commit 9f192242ddc974eddf281d1e8f72572c7f797e56
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Wed Feb 20 13:36:57 2013 +0100

    Improved Debug

    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
Backport of trunk fix to 3.2

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commit 61fd1334d24ec08ab29918a846573bb64b77cf41
Author: Christoph Paasch <christoph.paasch@uclouvain.be>
Date:   Wed Feb 20 19:55:29 2013 +0100

    Fix: dss-csum if a 64-bit dss option is present

    dss_off points to the beginning of the dss-option. If a 64-bit dss is
    present, we should skip the first 4 bytes, as they are added later with
    the final call to csum_partial.

    Reported-by: Erkrishna Khanal <erkrishna.khanal@gmail.com>
    Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>