ext4: Enable delalloc by default.

Enable delalloc by default to ensure it gets sufficient testing and
because it makes the filesystem much more efficient.  Add a nodealalloc
option to disable delayed allocation, and update ext4_show_options to
show delayed allocation off if it is disabled.

If the data=journal mount option is used, disable delayed allocation
since the delalloc code doesn't support data=journal yet.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>