zdtm unix_sock: don't use errno
zdtm unix_sock: don't use errno

In this place, errno is not being set and can be 0 or some random value,
so we should not use it. In case errno happens to be 0, we end up returning
a success status from a function while we should have returned a failure.

Signed-off-by: Kir Kolyshkin <c0159612b0ef32139322233232df1a0d189c4b9b@openvz.org>
Acked-by: Andrew Vagin <74c05afa918858348d6db8037d82fa8124870113@gmail.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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