xfs: reclaim speculative preallocations for append only files

xfs: reclaim speculative preallocations for append only files

The XFS XFS_DIFLAG_APPEND maps to the VFS S_APPEND flag, which forbids
writes that don't append at the current EOF.

But the commit originally adding XFS_DIFLAG_APPEND support (commit
a23321e766d in xfs xfs-import repository) also checked it to skip
releasing speculative preallocations, which doesn't make any sense.

Another commit (dd9f438e3290 in the xfs-import repository) later extended
that flag to also report these speculation preallocations which should
not exist in getbmap.

Remove these checks as nothing XFS_DIFLAG_APPEND implies that
preallocations beyond EOF should exist, but explicitly check for
XFS_DIFLAG_APPEND in xfs_file_release to bypass the algorithm that
discard preallocations on the first close as append only files aren't
expected to be written to only once.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>