Merge branch 'selftests-mptcp-join-fix-some-flaky-tests'

Matthieu Baerts says:

====================
selftests: mptcp: join: fix some flaky tests

When looking at the recent CI results on NIPA and MPTCP CIs, a few MPTCP
Join tests are marked as unstable. Here are some fixes for that.

- Patch 1: a small fix for mptcp_connect.sh, printing a note as
  initially intended. For >=v5.13.

- Patch 2: avoid unexpected reset when closing subflows. For >= 5.13.

- Patches 3-4: longer transfer when not waiting for the end. For >=5.18.

- Patch 5: read all received data when expecting a reset. For >= v6.1.

- Patch 6: a fix to properly kill background tasks. For >= v6.5.
====================

Link: https://patch.msgid.link/20251110-net-mptcp-sft-join-unstable-v1-0-a4332c714e10@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>