nilfs-clean: do not override min_reclaimable_blocks if -m option is not used

The current implementation of nilfs-clean always overrides
min_reclaimable_blocks parameter and nilfs_cleanerd cannot use that
value defined in /etc/nilfs_cleanerd.conf for manual-mode gc
operation.

This resolves the issue by avoiding to override the
min_reclaimable_blocks parameter when -m option is not specified.

Cc: Andreas Rohner <andreas.rohner@gmx.net>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
nilfs-clean: do not change min_reclaimable_blocks_unit in erroneous case

nilfs_clean_parse_min_reclaimable() function changes value of
min_reclaimable_blocks_unit even if a given percentage value is
invalid.  Although it doesn't cause any actual problems since its only
caller, nilfs_clean_parse_options(), will immediately abort the
program when nilfs_clean_parse_min_reclaimable() returned an error
status code (-1), it is not sane for
nilfs_clean_parse_min_reclaimable() function itself.

Cc: Andreas Rohner <andreas.rohner@gmx.net>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
nilfs_cleanerd.conf: try to use set_suinfo ioctl by default

Now set_suinfo ioctl is supported by nilfs2 kernel module in mainline.
This changes nilfs_cleanerd so that it tries to use the feature by
default.  If it's not supported by the underlying kernel, the feature
will be disabled automatically.

Cc: Andreas Rohner <andreas.rohner@gmx.net>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Temp commit