mkfs: distinguish between struct sb_feat_args and struct cli_params

mkfs: distinguish between struct sb_feat_args and struct cli_params

The struct sb_feat_args will actually be shared between the code which
processes command line options and the configuration file, as such we
need to clarify and reflect this clearly in documentation.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>