Merge branch 'mptcp-userspace-pm'

Matthieu Baerts says:

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mptcp: userspace pm: 'dump addrs' and 'get addr'

This series from Geliang adds two new Netlink commands to the userspace
PM:

- one to dump all addresses of a specific MPTCP connection:
  - feature added in patches 3 to 5
  - test added in patches 7, 8 and 10

- and one to get a specific address for an MPTCP connection:
  - feature added in patches 11 to 13
  - test added in patches 14 and 15

These new Netlink commands can be useful if an MPTCP daemon lost track
of the different connections, e.g. after having been restarted.

The other patches are some clean-ups and small improvements added
while working on the new features.

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Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>