selftests: mptcp: join: endpoints: longer transfer

selftests: mptcp: join: endpoints: longer transfer

In rare cases, when the test environment is very slow, some userspace
tests can fail because some expected events have not been seen.

Because the tests are expecting a long on-going connection, and they are
not waiting for the end of the transfer, it is fine to make the
connection longer. This connection will be killed at the end, after the
verifications, so making it longer doesn't change anything, apart from
avoid it to end before the end of the verifications

To play it safe, all endpoints tests not waiting for the end of the
transfer are now sharing a longer file (128KB) at slow speed.

Fixes: 69c6ce7b6eca ("selftests: mptcp: add implicit endpoint test case")
Cc: stable@vger.kernel.org
Fixes: e274f7154008 ("selftests: mptcp: add subflow limits test-cases")
Fixes: b5e2fb832f48 ("selftests: mptcp: add explicit test case for remove/readd")
Fixes: e06959e9eebd ("selftests: mptcp: join: test for flush/re-add endpoints")
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251110-net-mptcp-sft-join-unstable-v1-3-a4332c714e10@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>