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We used to simply take the first element from the stack after we have
split a network. That is wrong because it is not passing through any
filters and no further subnet checks. It could have therefore been
that the tree was not entirely flat.
Reported-by: Arne Fitzenreiter <arne_f@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>