rbd: set unmap limits based on object size
rbd: set unmap limits based on object size

rbd prefers unmaps that are aligned with the object size.

Signed-off-by: Mike Christie <39daeb1549a929782e38aa87c4e3da7f3844b09a@redhat.com>

open-iscsi/tcmu-runner,open-iscsi/tcmu-runner,agrover/tcmu-runner