xfs: refactor default quota grace period setting code

xfs: refactor default quota grace period setting code

Source kernel commit: ccc8e771aa7a80eb047fc263780816ca76dd02a6

Refactor the code that sets the default quota grace period into a helper
function so that we can override the ondisk behavior later.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>