Currently do_dump_one_inet_fd returns ret, but this variable is
overwritten a few times and it can be zero on error paths.

Use a separate variable for the function exit code. By default it is -1
and it is set to zero at the end. It's not changed anywere anywhere
except these two places.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>