selftests: Add duplicate config only for MD5 VRF tests

stable inclusion
from stable-v5.10.88
commit 5ba4dfb8b8a19d55811c399b9def7ffecfef559b
bugzilla: 186058 https://gitee.com/openeuler/kernel/issues/I4QW6A

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ba4dfb8b8a19d55811c399b9def7ffecfef559b



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[ Upstream commit 7e014759 ]

Commit referenced below added configuration in the default VRF that
duplicates a VRF to check MD5 passwords are properly used and fail
when expected. That config should not be added all the time as it
can cause tests to pass that should not (by matching on default VRF
setup when it should not). Move the duplicate setup to a function
that is only called for the MD5 tests and add a cleanup function
to remove it after the MD5 tests.

Fixes: 5cad8bce ("fcnal-test: Add TCP MD5 tests for VRF")
Signed-off-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>