test/librados: fix endian bugs in checksum test cases

test/librados: fix endian bugs in checksum test cases

We're seeing test failures when running rados/test.sh in Teuthology
on a big-endian platform (IBM Z).  These are all related to calls
to the checksum operations, which expect little-endian inputs and
outputs, but are in many places called with native-endian types
from the test code.

One test case, LibRadosAio::RoundTrip3 in aio.cc, already uses
ceph_le types to address this problem, and this test actually
completes successfully on IBM Z.  This patch changes the other
test case performing checksum operations accordingly.

With this patch in place, rados/test.sh now completed successfully.

Fixes: https://tracker.ceph.com/issues/47516
Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>