rcuja: lookup lower equal cannot reach dead-end

rcuja: lookup lower equal cannot reach dead-end

Thanks to the guarantees provided by ja_detach_node(), lookups can
_never_ see a branch that would lead to a dead-end. Therefore, lookup
lower/equal never needs to retry, and we thus have a bounded number of
operations for cds_ja_lookup_lower_equal().

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>