Multipath TCP part 3: MPTCPv1 (RFC 8684) support

These patches depend on the "Multipath TCP part 2: Single subflow"
patch set sent earlier.

In this set we add the necessary code for the RFC8684-style handshake.
RFC8684 obsoletes the experimental RFC6824 and makes MPTCP move-on to
version 1.

The MPTCP patchset exclusively supports RFC 8684. Although all MPTCP
deployments are currently based on RFC 6824, future deployments will be
migrating to MPTCP version 1. 3GPP's 5G standardization also solely supports
RFC 8684. Also, we believe that this initial submission of MPTCP will be
cleaner by solely supporting RFC 8684. If later on support for the old
MPTCP-version is required it can always be added in the future.

The major difference between RFC 8684 and RFC 6824 is that it has a better
support for servers using TCP SYN-cookies by reliably retransmitting the
MP_CAPABLE option.

Clone/fetch:
https://github.com/multipath-tcp/mptcp_net-next.git (tag: netdev-v1-part3)

Browse:
https://github.com/multipath-tcp/mptcp_net-next/tree/netdev-v1-part3

Thank you for your review. You can find us at mptcp@lists.01.org and
https://is.gd/mptcp_upstream.

Multipath TCP part 2: Single subflow

These patches depend on the "Multipath TCP part 1: Prerequisites" patch
set sent earlier.

This set adds MPTCP connection establishment, writing & reading MPTCP
options on data packets, a sysctl to allow MPTCP per-namespace, and self
tests. This is sufficient to establish and maintain a connection with a
MPTCP peer, but will not yet allow or initiate establishment of
additional MPTCP subflows.

Clone/fetch:
https://github.com/multipath-tcp/mptcp_net-next.git (tag: netdev-v1-part2)

Browse:
https://github.com/multipath-tcp/mptcp_net-next/tree/netdev-v1-part2

Thank you for your review. You can find us at mptcp@lists.01.org and
https://is.gd/mptcp_upstream

Multipath TCP part 4: Full dev branch

the last patches were not sent to netdev

Multipath TCP part 1: Prerequisites

The MPTCP upstreaming community has been collaborating on an
upstreamable MPTCP implementation that complies with RFC 8684. A minimal
set of features to comply with the specification involves a sizeable set
of code changes, so David requested that we split this work in to
multiple, smaller patch sets to build up MPTCP infrastructure.

The minimal MPTCP feature set we are proposing for the v5.6 timeframe is
split in to these parts for review:

Part 1 (this patch set): MPTCP prerequisites. Introduce some MPTCP
definitions, additional ULP and skb extension features, TCP option space
checking, and a few exported symbols.

Part 2: Single subflow implementation and self tests.

Part 3: Switch from MPTCP v0 (RFC 6824) to MPTCP v1 (new RFC 8684,
publication expected in the next few days).

Clone/fetch:
https://github.com/multipath-tcp/mptcp_net-next.git (tag: netdev-v1-part1)

Browse:
https://github.com/multipath-tcp/mptcp_net-next/tree/netdev-v1-part1

Thank you for your review. You can find us at mptcp@lists.01.org and
https://is.gd/mptcp_upstream

RFCv3 Full Patch-Set

RFCv3, full patch-set

Based on net-next: bacb7e1

RFCv3

RFCv3 sent to the netdev list, 2019-10-09

Based on net-next: bacb7e1

RFCv2

RFCv2 sent to the netdev list, 2019-10-02

ignore-v3

GitHub won't allow releases to be deleted - was starting to replace the ill-fated RFCv2 patch series, but based on maintainer feedback did not proceed.

RFCv1

RFC sent to the netdev list, 2019-06-17