libxfs: libxfs_buf_delwri_submit should write buffers immediately

libxfs: libxfs_buf_delwri_submit should write buffers immediately

The whole point of libxfs_buf_delwri_submit is to submit a bunch of
buffers for write and wait for the response.  Unfortunately, while it
does mark the buffers dirty, it doesn't actually flush them and lets the
cache mru flusher do it.  This is inconsistent with the kernel API,
which actually writes the buffers and returns any IO errors.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>