dm: disable WRITE SAME

dm: disable WRITE SAME

WRITE SAME bios are not yet handled correctly by device-mapper so
disable their use on device-mapper devices by setting
max_write_same_sectors to zero.

As an example, a ciphertext device is incompatible because the data
gets changed according to the location at which it written and so the
dm crypt target cannot support it.

Signed-off-by: Mike Snitzer <[email protected]>
Cc: [email protected]
Cc: Milan Broz <[email protected]>
Signed-off-by: Alasdair G Kergon <[email protected]>