lfstack: fix: add missing __cds_lfs_init

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Fix: lfstack reversed empty/non-empty return value

The return value of lfstack push operation is logically reversed
compared to the documentation, and compared to wfstack and wfcqueue.

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