xfs: Bump minimal size to 300M

xfs: Bump minimal size to 300M

From the xfsprogs source code:

* We don't support filesystems smaller than 300MB anymore.  Tiny
* filesystems have never been XFS' design target.  This limit has been
* carefully calculated to prevent formatting with a log smaller than
* the "realistic" size.
*
* If the realistic log size is 64MB, there are four AGs, and the log
* AG should be at least 1/8 free after formatting, this gives us:
*
* 64MB * (8 / 7) * 4 = 293MB

So let's accommodate and bump the minimal XFS filesystem size to 300M.