xfs: clean up bufsize alignment in xfs_ioc_attr_list

Use the round_down macro, and use the size of the uint32 type we
use in the callback that fills the buffer to make the code a little
more clear - the size of it is always the same as int for platforms
that Linux runs on.
Suggested-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_ioctl.c

@@ -415,7 +415,7 @@ xfs_ioc_attr_list(
 	context.resynch = 1;
 	context.attr_filter = xfs_attr_filter(flags);
 	context.buffer = buffer;
-	context.bufsize = (bufsize & ~(sizeof(int)-1));  /* align */
+	context.bufsize = round_down(bufsize, sizeof(uint32_t));
 	context.firstu = context.bufsize;
 	context.put_listent = xfs_ioc_attr_put_listent;