Merge branch 'selftests-mptcp-reduce-bufferbloat-and-cleanup'

Matthieu Baerts says:

====================
selftests: mptcp: reduce bufferbloat and cleanup

Bufferbloat is baaaad, even in our selftests: let's kill it (or at least
reduce it). By doing that, the tests (seem to) have a more stable
transfer, and are then less unstable. That's what patches 1-2 are doing,
and they can be backported up to 5.10.

Patch 3 is not related: a small fix in the selftests to remove temp
files that were not deleted in some conditions, since v5.13.
====================

Link: https://patch.msgid.link/20260527-net-mptcp-sft-bufferbloat-exit-v1-0-9afc4e742090@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>