selftests: mptcp: clean tmp files in simult_flows

stable inclusion
from stable-5.10.68
commit f450958f7ff8e99a3e511ae4732dbe67f54c5223
bugzilla: 182671 https://gitee.com/openeuler/kernel/issues/I4EWUH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f450958f7ff8e99a3e511ae4732dbe67f54c5223



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[ Upstream commit bfd862a7 ]

'$cin' and '$sin' variables are local to a function: they are then not
available from the cleanup trap.

Instead, we need to use '$large' and '$small' that are not local and
defined just before setting the trap.

Without this patch, running this script in a loop might cause a:

  write: No space left on device

issue.

Fixes: 1a418cb8 ("mptcp: simult flow self-tests")
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>