Merge branch 'mptcp-Improve-DATA_FIN-transmission'

Mat Martineau says:

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mptcp: Improve DATA_FIN transmission

MPTCP's DATA_FIN flag is sent in a DSS option when closing the
MPTCP-level connection. This patch series prepares for correct DATA_FIN
handling across multiple subflows (where individual subflows may
disconnect without closing the entire MPTCP connection) by changing the
way the MPTCP-level socket requests a DATA_FIN on a subflow and
propagates the necessary data for the TCP option.
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Signed-off-by: David S. Miller <davem@davemloft.net>