f2fs: directly add newly allocated pre-dirty nat entry to dirty set list

When we need to alloc nat entry and set it dirty, we can directly add it to
dirty set list(or initialize its list_head for new_ne) instead of adding it
to clean list and make a move. Introduce init_dirty flag to do it.

Signed-off-by: wangzijie <wangzijie1@honor.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>